Merge branch 'linus' into x86/urgent

Merge reason: We need the x86/uv updates from upstream, to queue up
              dependent fix.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

29 files changed, 1207 insertions, 555 deletions

diff --git a/Documentation/ABI/testing/debugfs-pktcdvd b/Documentation/ABI/testing/debugfs-pktcdvd
index bf9c16b..cf11736 100644
--- a/Documentation/ABI/testing/debugfs-pktcdvd
+++ b/Documentation/ABI/testing/debugfs-pktcdvd
@@ -1,4 +1,4 @@
-What:           /debug/pktcdvd/pktcdvd[0-7]
+What:           /sys/kernel/debug/pktcdvd/pktcdvd[0-7]
 Date:           Oct. 2006
 KernelVersion:  2.6.20
 Contact:        Thomas Maier <balagi@justmail.de>
@@ -10,10 +10,10 @@ debugfs interface
 The pktcdvd module (packet writing driver) creates
 these files in debugfs:
 
-/debug/pktcdvd/pktcdvd[0-7]/
+/sys/kernel/debug/pktcdvd/pktcdvd[0-7]/
     info            (0444) Lots of driver statistics and infos.
 
 Example:
 -------
 
-cat /debug/pktcdvd/pktcdvd0/info
+cat /sys/kernel/debug/pktcdvd/pktcdvd0/info
diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile
index a3a83d3..8918a32 100644
--- a/Documentation/DocBook/Makefile
+++ b/Documentation/DocBook/Makefile
@@ -31,7 +31,7 @@ PS_METHOD	= $(prefer-db2x)
 
 ###
 # The targets that may be used.
-PHONY += xmldocs sgmldocs psdocs pdfdocs htmldocs mandocs installmandocs
+PHONY += xmldocs sgmldocs psdocs pdfdocs htmldocs mandocs installmandocs cleandocs
 
 BOOKS := $(addprefix $(obj)/,$(DOCBOOKS))
 xmldocs: $(BOOKS)
@@ -213,11 +213,12 @@ silent_gen_xml = :
 dochelp:
 	@echo  ' Linux kernel internal documentation in different formats:'
 	@echo  '  htmldocs        - HTML'
-	@echo  '  installmandocs  - install man pages generated by mandocs'
-	@echo  '  mandocs         - man pages'
 	@echo  '  pdfdocs         - PDF'
 	@echo  '  psdocs          - Postscript'
 	@echo  '  xmldocs         - XML DocBook'
+	@echo  '  mandocs         - man pages'
+	@echo  '  installmandocs  - install man pages generated by mandocs'
+	@echo  '  cleandocs       - clean all generated DocBook files'
 
 ###
 # Temporary files left by various tools
@@ -235,6 +236,10 @@ clean-files := $(DOCBOOKS) \
 
 clean-dirs := $(patsubst %.xml,%,$(DOCBOOKS)) man
 
+cleandocs:
+	$(Q)rm -f $(call objectify, $(clean-files))
+	$(Q)rm -rf $(call objectify, $(clean-dirs))
+
 # Declare the contents of the .PHONY variable as phony.  We keep that
 # information in a variable se we can use it in if_changed and friends.
 
diff --git a/Documentation/block/biodoc.txt b/Documentation/block/biodoc.txt
index ecad6ee..6fab97e 100644
--- a/Documentation/block/biodoc.txt
+++ b/Documentation/block/biodoc.txt
@@ -1040,23 +1040,21 @@ Front merges are handled by the binary trees in AS and deadline schedulers.
 iii. Plugging the queue to batch requests in anticipation of opportunities for
      merge/sort optimizations
 
-This is just the same as in 2.4 so far, though per-device unplugging
-support is anticipated for 2.5. Also with a priority-based i/o scheduler,
-such decisions could be based on request priorities.
-
 Plugging is an approach that the current i/o scheduling algorithm resorts to so
 that it collects up enough requests in the queue to be able to take
 advantage of the sorting/merging logic in the elevator. If the
 queue is empty when a request comes in, then it plugs the request queue
-(sort of like plugging the bottom of a vessel to get fluid to build up)
+(sort of like plugging the bath tub of a vessel to get fluid to build up)
 till it fills up with a few more requests, before starting to service
 the requests. This provides an opportunity to merge/sort the requests before
 passing them down to the device. There are various conditions when the queue is
 unplugged (to open up the flow again), either through a scheduled task or
 could be on demand. For example wait_on_buffer sets the unplugging going
-(by running tq_disk) so the read gets satisfied soon. So in the read case,
-the queue gets explicitly unplugged as part of waiting for completion,
-in fact all queues get unplugged as a side-effect.
+through sync_buffer() running blk_run_address_space(mapping). Or the caller
+can do it explicity through blk_unplug(bdev). So in the read case,
+the queue gets explicitly unplugged as part of waiting for completion on that
+buffer. For page driven IO, the address space ->sync_page() takes care of
+doing the blk_run_address_space().
 
 Aside:
   This is kind of controversial territory, as it's not clear if plugging is
@@ -1067,11 +1065,6 @@ Aside:
   multi-page bios being queued in one shot, we may not need to wait to merge
   a big request from the broken up pieces coming by.
 
-  Per-queue granularity unplugging (still a Todo) may help reduce some of the
-  concerns with just a single tq_disk flush approach. Something like
-  blk_kick_queue() to unplug a specific queue (right away ?)
-  or optionally, all queues, is in the plan.
-
 4.4 I/O contexts
 I/O contexts provide a dynamically allocated per process data area. They may
 be used in I/O schedulers, and in the block layer (could be used for IO statis,
diff --git a/Documentation/cgroups/cpuacct.txt b/Documentation/cgroups/cpuacct.txt
index bb775fb..8b93094 100644
--- a/Documentation/cgroups/cpuacct.txt
+++ b/Documentation/cgroups/cpuacct.txt
@@ -30,3 +30,21 @@ The above steps create a new group g1 and move the current shell
 process (bash) into it. CPU time consumed by this bash and its children
 can be obtained from g1/cpuacct.usage and the same is accumulated in
 /cgroups/cpuacct.usage also.
+
+cpuacct.stat file lists a few statistics which further divide the
+CPU time obtained by the cgroup into user and system times. Currently
+the following statistics are supported:
+
+user: Time spent by tasks of the cgroup in user mode.
+system: Time spent by tasks of the cgroup in kernel mode.
+
+user and system are in USER_HZ unit.
+
+cpuacct controller uses percpu_counter interface to collect user and
+system times. This has two side effects:
+
+- It is theoretically possible to see wrong values for user and system times.
+  This is because percpu_counter_read() on 32bit systems isn't safe
+  against concurrent writes.
+- It is possible to see slightly outdated values for user and system times
+  due to the batch processing nature of percpu_counter.
diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
index a98a7fe..1a60887 100644
--- a/Documentation/cgroups/memory.txt
+++ b/Documentation/cgroups/memory.txt
@@ -6,15 +6,14 @@ used here with the memory controller that is used in hardware.
 
 Salient features
 
-a. Enable control of both RSS (mapped) and Page Cache (unmapped) pages
+a. Enable control of Anonymous, Page Cache (mapped and unmapped) and
+   Swap Cache memory pages.
 b. The infrastructure allows easy addition of other types of memory to control
 c. Provides *zero overhead* for non memory controller users
 d. Provides a double LRU: global memory pressure causes reclaim from the
    global LRU; a cgroup on hitting a limit, reclaims from the per
    cgroup LRU
 
-NOTE: Swap Cache (unmapped) is not accounted now.
-
 Benefits and Purpose of the memory controller
 
 The memory controller isolates the memory behaviour of a group of tasks
@@ -290,34 +289,44 @@ will be charged as a new owner of it.
   moved to the parent. If you want to avoid that, force_empty will be useful.
 
 5.2 stat file
-  memory.stat file includes following statistics (now)
-	cache			- # of pages from page-cache and shmem.
-	rss			- # of pages from anonymous memory.
-	pgpgin			- # of event of charging
-	pgpgout			- # of event of uncharging
-	active_anon		- # of pages on active lru of anon, shmem.
-	inactive_anon 		- # of pages on active lru of anon, shmem
-	active_file		- # of pages on active lru of file-cache
-	inactive_file		- # of pages on inactive lru of file cache
-	unevictable		- # of pages cannot be reclaimed.(mlocked etc)
-
-	Below is depend on CONFIG_DEBUG_VM.
-	inactive_ratio		- VM internal parameter. (see mm/page_alloc.c)
-	recent_rotated_anon	- VM internal parameter. (see mm/vmscan.c)
-	recent_rotated_file	- VM internal parameter. (see mm/vmscan.c)
-	recent_scanned_anon 	- VM internal parameter. (see mm/vmscan.c)
-	recent_scanned_file 	- VM internal parameter. (see mm/vmscan.c)
-
-  Memo:
+
+memory.stat file includes following statistics
+
+cache		- # of bytes of page cache memory.
+rss		- # of bytes of anonymous and swap cache memory.
+pgpgin		- # of pages paged in (equivalent to # of charging events).
+pgpgout		- # of pages paged out (equivalent to # of uncharging events).
+active_anon	- # of bytes of anonymous and  swap cache memory on active
+		  lru list.
+inactive_anon	- # of bytes of anonymous memory and swap cache memory on
+		  inactive lru list.
+active_file	- # of bytes of file-backed memory on active lru list.
+inactive_file	- # of bytes of file-backed memory on inactive lru list.
+unevictable	- # of bytes of memory that cannot be reclaimed (mlocked etc).
+
+The following additional stats are dependent on CONFIG_DEBUG_VM.
+
+inactive_ratio		- VM internal parameter. (see mm/page_alloc.c)
+recent_rotated_anon	- VM internal parameter. (see mm/vmscan.c)
+recent_rotated_file	- VM internal parameter. (see mm/vmscan.c)
+recent_scanned_anon	- VM internal parameter. (see mm/vmscan.c)
+recent_scanned_file	- VM internal parameter. (see mm/vmscan.c)
+
+Memo:
 	recent_rotated means recent frequency of lru rotation.
 	recent_scanned means recent # of scans to lru.
 	showing for better debug please see the code for meanings.
 
+Note:
+	Only anonymous and swap cache memory is listed as part of 'rss' stat.
+	This should not be confused with the true 'resident set size' or the
+	amount of physical memory used by the cgroup. Per-cgroup rss
+	accounting is not done yet.
 
 5.3 swappiness
   Similar to /proc/sys/vm/swappiness, but affecting a hierarchy of groups only.
 
-  Following cgroup's swapiness can't be changed.
+  Following cgroups' swapiness can't be changed.
   - root cgroup (uses /proc/sys/vm/swappiness).
   - a cgroup which uses hierarchy and it has child cgroup.
   - a cgroup which uses hierarchy and not the root of hierarchy.
diff --git a/Documentation/cgroups/resource_counter.txt b/Documentation/cgroups/resource_counter.txt
index f196ac1..95b24d7 100644
--- a/Documentation/cgroups/resource_counter.txt
+++ b/Documentation/cgroups/resource_counter.txt
@@ -47,13 +47,18 @@ to work with it.
 
 2. Basic accounting routines
 
- a. void res_counter_init(struct res_counter *rc)
+ a. void res_counter_init(struct res_counter *rc,
+				struct res_counter *rc_parent)
 
  	Initializes the resource counter. As usual, should be the first
 	routine called for a new counter.
 
- b. int res_counter_charge[_locked]
-			(struct res_counter *rc, unsigned long val)
+	The struct res_counter *parent can be used to define a hierarchical
+	child -> parent relationship directly in the res_counter structure,
+	NULL can be used to define no relationship.
+
+ c. int res_counter_charge(struct res_counter *rc, unsigned long val,
+				struct res_counter **limit_fail_at)
 
 	When a resource is about to be allocated it has to be accounted
 	with the appropriate resource counter (controller should determine
@@ -67,15 +72,25 @@ to work with it.
 	  * if the charging is performed first, then it should be uncharged
 	    on error path (if the one is called).
 
- c. void res_counter_uncharge[_locked]
+	If the charging fails and a hierarchical dependency exists, the
+	limit_fail_at parameter is set to the particular res_counter element
+	where the charging failed.
+
+ d. int res_counter_charge_locked
+			(struct res_counter *rc, unsigned long val)
+
+	The same as res_counter_charge(), but it must not acquire/release the
+	res_counter->lock internally (it must be called with res_counter->lock
+	held).
+
+ e. void res_counter_uncharge[_locked]
 			(struct res_counter *rc, unsigned long val)
 
 	When a resource is released (freed) it should be de-accounted
 	from the resource counter it was accounted to.  This is called
 	"uncharging".
 
-    The _locked routines imply that the res_counter->lock is taken.
-
+	The _locked routines imply that the res_counter->lock is taken.
 
  2.1 Other accounting routines
 
diff --git a/Documentation/driver-model/platform.txt b/Documentation/driver-model/platform.txt
index 83009fdc..2e2c2ea 100644
--- a/Documentation/driver-model/platform.txt
+++ b/Documentation/driver-model/platform.txt
@@ -169,3 +169,62 @@ three different ways to find such a match:
       be probed later if another device registers.  (Which is OK, since
       this interface is only for use with non-hotpluggable devices.)
 
+
+Early Platform Devices and Drivers
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The early platform interfaces provide platform data to platform device
+drivers early on during the system boot. The code is built on top of the
+early_param() command line parsing and can be executed very early on.
+
+Example: "earlyprintk" class early serial console in 6 steps
+
+1. Registering early platform device data
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The architecture code registers platform device data using the function
+early_platform_add_devices(). In the case of early serial console this
+should be hardware configuration for the serial port. Devices registered
+at this point will later on be matched against early platform drivers.
+
+2. Parsing kernel command line
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The architecture code calls parse_early_param() to parse the kernel
+command line. This will execute all matching early_param() callbacks.
+User specified early platform devices will be registered at this point.
+For the early serial console case the user can specify port on the
+kernel command line as "earlyprintk=serial.0" where "earlyprintk" is
+the class string, "serial" is the name of the platfrom driver and
+0 is the platform device id. If the id is -1 then the dot and the
+id can be omitted.
+
+3. Installing early platform drivers belonging to a certain class
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The architecture code may optionally force registration of all early
+platform drivers belonging to a certain class using the function
+early_platform_driver_register_all(). User specified devices from
+step 2 have priority over these. This step is omitted by the serial
+driver example since the early serial driver code should be disabled
+unless the user has specified port on the kernel command line.
+
+4. Early platform driver registration
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Compiled-in platform drivers making use of early_platform_init() are
+automatically registered during step 2 or 3. The serial driver example
+should use early_platform_init("earlyprintk", &platform_driver).
+
+5. Probing of early platform drivers belonging to a certain class
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The architecture code calls early_platform_driver_probe() to match
+registered early platform devices associated with a certain class with
+registered early platform drivers. Matched devices will get probed().
+This step can be executed at any point during the early boot. As soon
+as possible may be good for the serial port case.
+
+6. Inside the early platform driver probe()
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The driver code needs to take special care during early boot, especially
+when it comes to memory allocation and interrupt registration. The code
+in the probe() function can use is_early_platform_device() to check if
+it is called at early platform device or at the regular platform device
+time. The early serial driver performs register_console() at this point.
+
+For further information, see <linux/platform_device.h>.
diff --git a/Documentation/feature-removal-schedule.txt b/Documentation/feature-removal-schedule.txt
index 7e2af10..de491a3 100644
--- a/Documentation/feature-removal-schedule.txt
+++ b/Documentation/feature-removal-schedule.txt
@@ -428,3 +428,12 @@ Why:	In 2.6.27, the semantics of /sys/bus/pci/slots was redefined to
 	After a reasonable transition period, we will remove the legacy
 	fakephp interface.
 Who:	Alex Chiang <achiang@hp.com>
+
+---------------------------
+
+What:	i2c-voodoo3 driver
+When:	October 2009
+Why:	Superseded by tdfxfb. I2C/DDC support used to live in a separate
+	driver but this caused driver conflicts.
+Who:	Jean Delvare <khali@linux-fr.org>
+	Krzysztof Helt <krzysztof.h1@wp.pl>
diff --git a/Documentation/filesystems/pohmelfs/design_notes.txt b/Documentation/filesystems/pohmelfs/design_notes.txt
index 6d6db60..dcf8335 100644
--- a/Documentation/filesystems/pohmelfs/design_notes.txt
+++ b/Documentation/filesystems/pohmelfs/design_notes.txt
@@ -56,9 +56,10 @@ workloads and can fully utilize the bandwidth to the servers when doing bulk
 data transfers.
 
 POHMELFS clients operate with a working set of servers and are capable of balancing read-only
-operations (like lookups or directory listings) between them.
+operations (like lookups or directory listings) between them according to IO priorities.
 Administrators can add or remove servers from the set at run-time via special commands (described
-in Documentation/pohmelfs/info.txt file). Writes are replicated to all servers.
+in Documentation/pohmelfs/info.txt file). Writes are replicated to all servers, which are connected
+with write permission turned on. IO priority and permissions can be changed in run-time.
 
 POHMELFS is capable of full data channel encryption and/or strong crypto hashing.
 One can select any kernel supported cipher, encryption mode, hash type and operation mode
diff --git a/Documentation/filesystems/pohmelfs/info.txt b/Documentation/filesystems/pohmelfs/info.txt
index 4e3d501..db2e413 100644
--- a/Documentation/filesystems/pohmelfs/info.txt
+++ b/Documentation/filesystems/pohmelfs/info.txt
@@ -1,6 +1,8 @@
 POHMELFS usage information.
 
-Mount options:
+Mount options.
+All but index, number of crypto threads and maximum IO size can changed via remount.
+
 idx=%u
  Each mountpoint is associated with a special index via this option.
  Administrator can add or remove servers from the given index, so all mounts,
@@ -52,16 +54,27 @@ mcache_timeout=%u
 
 Usage examples.
 
-Add (or remove if it already exists) server server1.net:1025 into the working set with index $idx
+Add server server1.net:1025 into the working set with index $idx
 with appropriate hash algorithm and key file and cipher algorithm, mode and key file:
-$cfg -a server1.net -p 1025 -i $idx -K $hash_key -k $cipher_key
+$cfg A add -a server1.net -p 1025 -i $idx -K $hash_key -k $cipher_key
 
 Mount filesystem with given index $idx to /mnt mountpoint.
 Client will connect to all servers specified in the working set via previous command:
 mount -t pohmel -o idx=$idx q /mnt
 
-One can add or remove servers from working set after mounting too.
+Change permissions to read-only (-I 1 option, '-I 2' - write-only, 3 - rw):
+$cfg A modify -a server1.net -p 1025 -i $idx -I 1
+
+Change IO priority to 123 (node with the highest priority gets read requests).
+$cfg A modify -a server1.net -p 1025 -i $idx -P 123
 
+One can check currect status of all connections in the mountstats file:
+# cat /proc/$PID/mountstats
+...
+device none mounted on /mnt with fstype pohmel
+idx addr(:port) socket_type protocol active priority permissions
+0 server1.net:1026 1 6 1 250 1
+0 server2.net:1025 1 6 1 123 3
 
 Server installation.
 
diff --git a/Documentation/infiniband/ipoib.txt b/Documentation/infiniband/ipoib.txt
index 864ff32..6d40f00 100644
--- a/Documentation/infiniband/ipoib.txt
+++ b/Documentation/infiniband/ipoib.txt
@@ -24,6 +24,49 @@ Partitions and P_Keys
   The P_Key for any interface is given by the "pkey" file, and the
   main interface for a subinterface is in "parent."
 
+Datagram vs Connected modes
+
+  The IPoIB driver supports two modes of operation: datagram and
+  connected.  The mode is set and read through an interface's
+  /sys/class/net/<intf name>/mode file.
+
+  In datagram mode, the IB UD (Unreliable Datagram) transport is used
+  and so the interface MTU has is equal to the IB L2 MTU minus the
+  IPoIB encapsulation header (4 bytes).  For example, in a typical IB
+  fabric with a 2K MTU, the IPoIB MTU will be 2048 - 4 = 2044 bytes.
+
+  In connected mode, the IB RC (Reliable Connected) transport is used.
+  Connected mode is to takes advantage of the connected nature of the
+  IB transport and allows an MTU up to the maximal IP packet size of
+  64K, which reduces the number of IP packets needed for handling
+  large UDP datagrams, TCP segments, etc and increases the performance
+  for large messages.
+
+  In connected mode, the interface's UD QP is still used for multicast
+  and communication with peers that don't support connected mode. In
+  this case, RX emulation of ICMP PMTU packets is used to cause the
+  networking stack to use the smaller UD MTU for these neighbours.
+
+Stateless offloads
+
+  If the IB HW supports IPoIB stateless offloads, IPoIB advertises
+  TCP/IP checksum and/or Large Send (LSO) offloading capability to the
+  network stack.
+
+  Large Receive (LRO) offloading is also implemented and may be turned
+  on/off using ethtool calls.  Currently LRO is supported only for
+  checksum offload capable devices.
+
+  Stateless offloads are supported only in datagram mode.  
+
+Interrupt moderation
+
+  If the underlying IB device supports CQ event moderation, one can
+  use ethtool to set interrupt mitigation parameters and thus reduce
+  the overhead incurred by handling interrupts.  The main code path of
+  IPoIB doesn't use events for TX completion signaling so only RX
+  moderation is supported.
+
 Debugging Information
 
   By compiling the IPoIB driver with CONFIG_INFINIBAND_IPOIB_DEBUG set
@@ -55,3 +98,5 @@ References
     http://ietf.org/rfc/rfc4391.txt 
   IP over InfiniBand (IPoIB) Architecture (RFC 4392)
     http://ietf.org/rfc/rfc4392.txt 
+  IP over InfiniBand: Connected Mode (RFC 4755)
+    http://ietf.org/rfc/rfc4755.txt
diff --git a/Documentation/input/rotary-encoder.txt b/Documentation/input/rotary-encoder.txt
new file mode 100644
index 0000000..435102a
--- /dev/null
+++ b/Documentation/input/rotary-encoder.txt
@@ -0,0 +1,101 @@
+rotary-encoder - a generic driver for GPIO connected devices
+Daniel Mack <daniel@caiaq.de>, Feb 2009
+
+0. Function
+-----------
+
+Rotary encoders are devices which are connected to the CPU or other
+peripherals with two wires. The outputs are phase-shifted by 90 degrees
+and by triggering on falling and rising edges, the turn direction can
+be determined.
+
+The phase diagram of these two outputs look like this:
+
+                  _____       _____       _____
+                 |     |     |     |     |     |
+  Channel A  ____|     |_____|     |_____|     |____
+
+                 :  :  :  :  :  :  :  :  :  :  :  :
+            __       _____       _____       _____
+              |     |     |     |     |     |     |
+  Channel B   |_____|     |_____|     |_____|     |__
+
+                 :  :  :  :  :  :  :  :  :  :  :  :
+  Event          a  b  c  d  a  b  c  d  a  b  c  d
+
+                |<-------->|
+	          one step
+
+
+For more information, please see
+	http://en.wikipedia.org/wiki/Rotary_encoder
+
+
+1. Events / state machine
+-------------------------
+
+a) Rising edge on channel A, channel B in low state
+	This state is used to recognize a clockwise turn
+
+b) Rising edge on channel B, channel A in high state
+	When entering this state, the encoder is put into 'armed' state,
+	meaning that there it has seen half the way of a one-step transition.
+
+c) Falling edge on channel A, channel B in high state
+	This state is used to recognize a counter-clockwise turn
+
+d) Falling edge on channel B, channel A in low state
+	Parking position. If the encoder enters this state, a full transition
+	should have happend, unless it flipped back on half the way. The
+	'armed' state tells us about that.
+
+2. Platform requirements
+------------------------
+
+As there is no hardware dependent call in this driver, the platform it is
+used with must support gpiolib. Another requirement is that IRQs must be
+able to fire on both edges.
+
+
+3. Board integration
+--------------------
+
+To use this driver in your system, register a platform_device with the
+name 'rotary-encoder' and associate the IRQs and some specific platform
+data with it.
+
+struct rotary_encoder_platform_data is declared in
+include/linux/rotary-encoder.h and needs to be filled with the number of
+steps the encoder has and can carry information about externally inverted
+signals (because of used invertig buffer or other reasons).
+
+Because GPIO to IRQ mapping is platform specific, this information must
+be given in seperately to the driver. See the example below.
+
+---------<snip>---------
+
+/* board support file example */
+
+#include <linux/input.h>
+#include <linux/rotary_encoder.h>
+
+#define GPIO_ROTARY_A 1
+#define GPIO_ROTARY_B 2
+
+static struct rotary_encoder_platform_data my_rotary_encoder_info = {
+	.steps		= 24,
+	.axis		= ABS_X,
+	.gpio_a		= GPIO_ROTARY_A,
+	.gpio_b		= GPIO_ROTARY_B,
+	.inverted_a	= 0,
+	.inverted_b	= 0,
+};
+
+static struct platform_device rotary_encoder_device = {
+	.name		= "rotary-encoder",
+	.id		= 0,
+	.dev		= {
+		.platform_data = &my_rotary_encoder_info,
+	}
+};
+
diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt
index 51104f9..d76cfd8 100644
--- a/Documentation/kbuild/makefiles.txt
+++ b/Documentation/kbuild/makefiles.txt
@@ -40,10 +40,16 @@ This document describes the Linux kernel Makefiles.
 	   --- 6.7 Custom kbuild commands
 	   --- 6.8 Preprocessing linker scripts
 
-	=== 7 Kbuild Variables
-	=== 8 Makefile language
-	=== 9 Credits
-	=== 10 TODO
+	=== 7 Kbuild syntax for exported headers
+		--- 7.1 header-y
+		--- 7.2 objhdr-y
+		--- 7.3 destination-y
+		--- 7.4 unifdef-y (deprecated)
+
+	=== 8 Kbuild Variables
+	=== 9 Makefile language
+	=== 10 Credits
+	=== 11 TODO
 
 === 1 Overview
 
@@ -310,6 +316,16 @@ more details, with real examples.
 		#arch/m68k/fpsp040/Makefile
 		ldflags-y := -x
 
+    subdir-ccflags-y, subdir-asflags-y
+	The two flags listed above are similar to ccflags-y and as-falgs-y.
+	The difference is that the subdir- variants has effect for the kbuild
+	file where tey are present and all subdirectories.
+	Options specified using subdir-* are added to the commandline before
+	the options specified using the non-subdir variants.
+
+	Example:
+		subdir-ccflags-y := -Werror
+
     CFLAGS_$@, AFLAGS_$@
 
 	CFLAGS_$@ and AFLAGS_$@ only apply to commands in current
@@ -1143,8 +1159,69 @@ When kbuild executes, the following steps are followed (roughly):
 	The kbuild infrastructure for *lds file are used in several
 	architecture-specific files.
 
+=== 7 Kbuild syntax for exported headers
+
+The kernel include a set of headers that is exported to userspace.
+Many headers can be exported as-is but other headers requires  a
+minimal pre-processing before they are ready for user-space.
+The pre-processing does:
+- drop kernel specific annotations
+- drop include of compiler.h
+- drop all sections that is kernel internat (guarded by ifdef __KERNEL__)
+
+Each relevant directory contain a file name "Kbuild" which specify the
+headers to be exported.
+See subsequent chapter for the syntax of the Kbuild file.
+
+	--- 7.1 header-y
+
+	header-y specify header files to be exported.
+
+		Example:
+			#include/linux/Kbuild
+			header-y += usb/
+			header-y += aio_abi.h
+
+	The convention is to list one file per line and
+	preferably in alphabetic order.
+
+	header-y also specify which subdirectories to visit.
+	A subdirectory is identified by a trailing '/' which
+	can be seen in the example above for the usb subdirectory.
+
+	Subdirectories are visited before their parent directories.
+
+	--- 7.2 objhdr-y
+
+	objhdr-y specifies generated files to be exported.
+	Generated files are special as they need to be looked
+	up in another directory when doing 'make O=...' builds.
+
+		Example:
+			#include/linux/Kbuild
+			objhdr-y += version.h
+
+	--- 7.3 destination-y
+
+	When an architecture have a set of exported headers that needs to be
+	exported to a different directory destination-y is used.
+	destination-y specify the destination directory for all exported
+	headers in the file where it is present.
+
+		Example:
+			#arch/xtensa/platforms/s6105/include/platform/Kbuild
+			destination-y := include/linux
+
+	In the example above all exported headers in the Kbuild file
+	will be located in the directory "include/linux" when exported.
+
+
+	--- 7.4 unifdef-y (deprecated)
+
+	unifdef-y is deprecated. A direct replacement is header-y.
+
 
-=== 7 Kbuild Variables
+=== 8 Kbuild Variables
 
 The top Makefile exports the following variables:
 
@@ -1206,7 +1283,7 @@ The top Makefile exports the following variables:
 	INSTALL_MOD_STRIP will used as the option(s) to the strip command.
 
 
-=== 8 Makefile language
+=== 9 Makefile language
 
 The kernel Makefiles are designed to be run with GNU Make.  The Makefiles
 use only the documented features of GNU Make, but they do use many
@@ -1225,14 +1302,14 @@ time the left-hand side is used.
 There are some cases where "=" is appropriate.  Usually, though, ":="
 is the right choice.
 
-=== 9 Credits
+=== 10 Credits
 
 Original version made by Michael Elizabeth Chastain, <mailto:mec@shout.net>
 Updates by Kai Germaschewski <kai@tp1.ruhr-uni-bochum.de>
 Updates by Sam Ravnborg <sam@ravnborg.org>
 Language QA by Jan Engelhardt <jengelh@gmx.de>
 
-=== 10 TODO
+=== 11 TODO
 
 - Describe how kbuild supports shipped files with _shipped.
 - Generating offset header files.
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 9e4fe72..90b3924 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -231,6 +231,35 @@ and is between 256 and 4096 characters. It is defined in the file
  			power state again in power transition.
  			1 : disable the power state check
 
+	acpi_sci=	[HW,ACPI] ACPI System Control Interrupt trigger mode
+			Format: { level | edge | high | low }
+
+	acpi_serialize	[HW,ACPI] force serialization of AML methods
+
+	acpi_skip_timer_override [HW,ACPI]
+			Recognize and ignore IRQ0/pin2 Interrupt Override.
+			For broken nForce2 BIOS resulting in XT-PIC timer.
+
+	acpi_sleep=	[HW,ACPI] Sleep options
+			Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
+				  old_ordering, s4_nonvs }
+			See Documentation/power/video.txt for information on
+			s3_bios and s3_mode.
+			s3_beep is for debugging; it makes the PC's speaker beep
+			as soon as the kernel's real-mode entry point is called.
+			s4_nohwsig prevents ACPI hardware signature from being
+			used during resume from hibernation.
+			old_ordering causes the ACPI 1.0 ordering of the _PTS
+			control method, with respect to putting devices into
+			low power states, to be enforced (the ACPI 2.0 ordering
+			of _PTS is used by default).
+			s4_nonvs prevents the kernel from saving/restoring the
+			ACPI NVS memory during hibernation.
+
+	acpi_use_timer_override [HW,ACPI]
+			Use timer override. For some broken Nvidia NF5 boards
+			that require a timer override, but don't have HPET
+
 	acpi_enforce_resources=	[ACPI]
 			{ strict | lax | no }
 			Check for resource conflicts between native drivers
@@ -250,6 +279,9 @@ and is between 256 and 4096 characters. It is defined in the file
 	ad1848=		[HW,OSS]
 			Format: <io>,<irq>,<dma>,<dma2>,<type>
 
+	add_efi_memmap	[EFI; X86] Include EFI memory map in
+			kernel's map of available physical RAM.
+
 	advansys=	[HW,SCSI]
 			See header of drivers/scsi/advansys.c.
 
@@ -1840,6 +1872,12 @@ and is between 256 and 4096 characters. It is defined in the file
 			autoconfiguration.
 			Ranges are in pairs (memory base and size).
 
+	ports=		[IP_VS_FTP] IPVS ftp helper module
+			Default is 21.
+			Up to 8 (IP_VS_APP_MAX_PORTS) ports
+			may be specified.
+			Format: <port>,<port>....
+
 	print-fatal-signals=
 			[KNL] debug: print fatal signals
 			print-fatal-signals=1: print segfault info to
diff --git a/Documentation/lguest/.gitignore b/Documentation/lguest/.gitignore
new file mode 100644
index 0000000..115587f
--- /dev/null
+++ b/Documentation/lguest/.gitignore
@@ -0,0 +1 @@
+lguest
diff --git a/Documentation/lguest/lguest.txt b/Documentation/lguest/lguest.txt
index 29510dc..28c7473 100644
--- a/Documentation/lguest/lguest.txt
+++ b/Documentation/lguest/lguest.txt
@@ -3,11 +3,11 @@
  /,    /`      - or, A Young Coder's Illustrated Hypervisor
  \\"--\\    http://lguest.ozlabs.org
 
-Lguest is designed to be a minimal hypervisor for the Linux kernel, for
-Linux developers and users to experiment with virtualization with the
-minimum of complexity.  Nonetheless, it should have sufficient
-features to make it useful for specific tasks, and, of course, you are
-encouraged to fork and enhance it (see drivers/lguest/README).
+Lguest is designed to be a minimal 32-bit x86 hypervisor for the Linux kernel,
+for Linux developers and users to experiment with virtualization with the
+minimum of complexity.  Nonetheless, it should have sufficient features to
+make it useful for specific tasks, and, of course, you are encouraged to fork
+and enhance it (see drivers/lguest/README).
 
 Features:
 
@@ -37,6 +37,7 @@ Running Lguest:
      "Paravirtualized guest support" = Y
         "Lguest guest support" = Y
      "High Memory Support" = off/4GB
+     "PAE (Physical Address Extension) Support" = N
      "Alignment value to which kernel should be aligned" = 0x100000
         (CONFIG_PARAVIRT=y, CONFIG_LGUEST_GUEST=y, CONFIG_HIGHMEM64G=n and
          CONFIG_PHYSICAL_ALIGN=0x100000)
diff --git a/Documentation/networking/bonding.txt b/Documentation/networking/bonding.txt
index 5ede747..0876275 100644
--- a/Documentation/networking/bonding.txt
+++ b/Documentation/networking/bonding.txt
@@ -1242,7 +1242,7 @@ monitoring is enabled, and vice-versa.
 To add ARP targets:
 # echo +192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target
 # echo +192.168.0.101 > /sys/class/net/bond0/bonding/arp_ip_target
-	NOTE:  up to 10 target addresses may be specified.
+	NOTE:  up to 16 target addresses may be specified.
 
 To remove an ARP target:
 # echo -192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target
diff --git a/Documentation/powerpc/dts-bindings/fsl/i2c.txt b/Documentation/powerpc/dts-bindings/fsl/i2c.txt
index d0ab33e..b6d2e21 100644
--- a/Documentation/powerpc/dts-bindings/fsl/i2c.txt
+++ b/Documentation/powerpc/dts-bindings/fsl/i2c.txt
@@ -7,8 +7,10 @@ Required properties :
 
 Recommended properties :
 
- - compatible : Should be "fsl-i2c" for parts compatible with
-   Freescale I2C specifications.
+ - compatible : compatibility list with 2 entries, the first should
+   be "fsl,CHIP-i2c" where CHIP is the name of a compatible processor,
+   e.g. mpc8313, mpc8543, mpc8544, mpc5200 or mpc5200b. The second one
+   should be "fsl-i2c".
  - interrupts : <a b> where a is the interrupt number and b is a
    field that represents an encoding of the sense and level
    information for the interrupt.  This should be encoded based on
@@ -16,17 +18,31 @@ Recommended properties :
    controller you have.
  - interrupt-parent : the phandle for the interrupt controller that
    services interrupts for this device.
- - dfsrr : boolean; if defined, indicates that this I2C device has
-   a digital filter sampling rate register
- - fsl5200-clocking : boolean; if defined, indicated that this device
-   uses the FSL 5200 clocking mechanism.
-
-Example :
-	i2c@3000 {
-		interrupt-parent = <40000>;
-		interrupts = <1b 3>;
-		reg = <3000 18>;
-		device_type = "i2c";
-		compatible  = "fsl-i2c";
-		dfsrr;
+ - fsl,preserve-clocking : boolean; if defined, the clock settings
+   from the bootloader are preserved (not touched).
+ - clock-frequency : desired I2C bus clock frequency in Hz.
+
+Examples :
+
+	i2c@3d00 {
+		#address-cells = <1>;
+		#size-cells = <0>;
+		compatible = "fsl,mpc5200b-i2c","fsl,mpc5200-i2c","fsl-i2c";
+		cell-index = <0>;
+		reg = <0x3d00 0x40>;
+		interrupts = <2 15 0>;
+		interrupt-parent = <&mpc5200_pic>;
+		fsl,preserve-clocking;
 	};
+
+	i2c@3100 {
+		#address-cells = <1>;
+		#size-cells = <0>;
+		cell-index = <1>;
+		compatible = "fsl,mpc8544-i2c", "fsl-i2c";
+		reg = <0x3100 0x100>;
+		interrupts = <43 2>;
+		interrupt-parent = <&mpic>;
+		clock-frequency = <400000>;
+	};
+
diff --git a/Documentation/sound/alsa/HD-Audio.txt b/Documentation/sound/alsa/HD-Audio.txt
index c5948f2..88b7433 100644
--- a/Documentation/sound/alsa/HD-Audio.txt
+++ b/Documentation/sound/alsa/HD-Audio.txt
@@ -169,7 +169,7 @@ PCI SSID look-up.
 What `model` option values are available depends on the codec chip.
 Check your codec chip from the codec proc file (see "Codec Proc-File"
 section below).  It will show the vendor/product name of your codec
-chip.  Then, see Documentation/sound/alsa/HD-Audio-Modelstxt file,
+chip.  Then, see Documentation/sound/alsa/HD-Audio-Models.txt file,
 the section of HD-audio driver.  You can find a list of codecs
 and `model` options belonging to each codec.  For example, for Realtek
 ALC262 codec chip, pass `model=ultra` for devices that are compatible
@@ -177,7 +177,7 @@ with Samsung Q1 Ultra.
 
 Thus, the first thing you can do for any brand-new, unsupported and
 non-working HD-audio hardware is to check HD-audio codec and several
-different `model` option values.  If you have a luck, some of them
+different `model` option values.  If you have any luck, some of them
 might suit with your device well.
 
 Some codecs such as ALC880 have a special model option `model=test`.
diff --git a/Documentation/sparse.txt b/Documentation/sparse.txt
index 42f43fa..34c76a5 100644
--- a/Documentation/sparse.txt
+++ b/Documentation/sparse.txt
@@ -42,6 +42,14 @@ sure that bitwise types don't get mixed up (little-endian vs big-endian
 vs cpu-endian vs whatever), and there the constant "0" really _is_
 special.
 
+__bitwise__ - to be used for relatively compact stuff (gfp_t, etc.) that
+is mostly warning-free and is supposed to stay that way.  Warnings will
+be generated without __CHECK_ENDIAN__.
+
+__bitwise - noisy stuff; in particular, __le*/__be* are that.  We really
+don't want to drown in noise unless we'd explicitly asked for it.
+
+
 Getting sparse
 ~~~~~~~~~~~~~~
 
diff --git a/Documentation/sysctl/net.txt b/Documentation/sysctl/net.txt
index a34d55b..df38ef0 100644
--- a/Documentation/sysctl/net.txt
+++ b/Documentation/sysctl/net.txt
@@ -95,7 +95,7 @@ of struct cmsghdr structures with appended data.
 
 There is only one file in this directory.
 unix_dgram_qlen limits the max number of datagrams queued in Unix domain
-socket's buffer. It will not take effect unless PF_UNIX flag is spicified.
+socket's buffer. It will not take effect unless PF_UNIX flag is specified.
 
 
 3. /proc/sys/net/ipv4 - IPV4 settings
diff --git a/Documentation/tomoyo.txt b/Documentation/tomoyo.txt
new file mode 100644
index 0000000..b3a232c
--- /dev/null
+++ b/Documentation/tomoyo.txt
@@ -0,0 +1,55 @@
+--- What is TOMOYO? ---
+
+TOMOYO is a name-based MAC extension (LSM module) for the Linux kernel.
+
+LiveCD-based tutorials are available at
+http://tomoyo.sourceforge.jp/en/1.6.x/1st-step/ubuntu8.04-live/
+http://tomoyo.sourceforge.jp/en/1.6.x/1st-step/centos5-live/ .
+Though these tutorials use non-LSM version of TOMOYO, they are useful for you
+to know what TOMOYO is.
+
+--- How to enable TOMOYO? ---
+
+Build the kernel with CONFIG_SECURITY_TOMOYO=y and pass "security=tomoyo" on
+kernel's command line.
+
+Please see http://tomoyo.sourceforge.jp/en/2.2.x/ for details.
+
+--- Where is documentation? ---
+
+User <-> Kernel interface documentation is available at
+http://tomoyo.sourceforge.jp/en/2.2.x/policy-reference.html .
+
+Materials we prepared for seminars and symposiums are available at
+http://sourceforge.jp/projects/tomoyo/docs/?category_id=532&language_id=1 .
+Below lists are chosen from three aspects.
+
+What is TOMOYO?
+  TOMOYO Linux Overview
+    http://sourceforge.jp/projects/tomoyo/docs/lca2009-takeda.pdf
+  TOMOYO Linux: pragmatic and manageable security for Linux
+    http://sourceforge.jp/projects/tomoyo/docs/freedomhectaipei-tomoyo.pdf
+  TOMOYO Linux: A Practical Method to Understand and Protect Your Own Linux Box
+    http://sourceforge.jp/projects/tomoyo/docs/PacSec2007-en-no-demo.pdf
+
+What can TOMOYO do?
+  Deep inside TOMOYO Linux
+    http://sourceforge.jp/projects/tomoyo/docs/lca2009-kumaneko.pdf
+  The role of "pathname based access control" in security.
+    http://sourceforge.jp/projects/tomoyo/docs/lfj2008-bof.pdf
+
+History of TOMOYO?
+  Realities of Mainlining
+    http://sourceforge.jp/projects/tomoyo/docs/lfj2008.pdf
+
+--- What is future plan? ---
+
+We believe that inode based security and name based security are complementary
+and both should be used together. But unfortunately, so far, we cannot enable
+multiple LSM modules at the same time. We feel sorry that you have to give up
+SELinux/SMACK/AppArmor etc. when you want to use TOMOYO.
+
+We hope that LSM becomes stackable in future. Meanwhile, you can use non-LSM
+version of TOMOYO, available at http://tomoyo.sourceforge.jp/en/1.6.x/ .
+LSM version of TOMOYO is a subset of non-LSM version of TOMOYO. We are planning
+to port non-LSM version's functionalities to LSM versions.
diff --git a/Documentation/ftrace.txt b/Documentation/trace/ftrace.txt
index fd9a3e6..fd9a3e6 100644
--- a/Documentation/ftrace.txt
+++ b/Documentation/trace/ftrace.txt
diff --git a/Documentation/vm/kmemtrace.txt b/Documentation/trace/kmemtrace.txt
index a956d9b..a956d9b 100644
--- a/Documentation/vm/kmemtrace.txt
+++ b/Documentation/trace/kmemtrace.txt
diff --git a/Documentation/tracers/mmiotrace.txt b/Documentation/trace/mmiotrace.txt
index 5731c67..5731c67 100644
--- a/Documentation/tracers/mmiotrace.txt
+++ b/Documentation/trace/mmiotrace.txt
diff --git a/Documentation/tracepoints.txt b/Documentation/trace/tracepoints.txt
index c0e1cee..c0e1cee 100644
--- a/Documentation/tracepoints.txt
+++ b/Documentation/trace/tracepoints.txt
diff --git a/Documentation/vm/00-INDEX b/Documentation/vm/00-INDEX
index 2131b00..2f77ced 100644
--- a/Documentation/vm/00-INDEX
+++ b/Documentation/vm/00-INDEX
@@ -1,5 +1,7 @@
 00-INDEX
 	- this file.
+active_mm.txt
+	- An explanation from Linus about tsk->active_mm vs tsk->mm.
 balance
 	- various information on memory balancing.
 hugetlbpage.txt
diff --git a/Documentation/vm/active_mm.txt b/Documentation/vm/active_mm.txt
new file mode 100644
index 0000000..4ee1f64
--- /dev/null
+++ b/Documentation/vm/active_mm.txt
@@ -0,0 +1,83 @@
+List:       linux-kernel
+Subject:    Re: active_mm
+From:       Linus Torvalds <torvalds () transmeta ! com>
+Date:       1999-07-30 21:36:24
+
+Cc'd to linux-kernel, because I don't write explanations all that often,
+and when I do I feel better about more people reading them.
+
+On Fri, 30 Jul 1999, David Mosberger wrote:
+>
+> Is there a brief description someplace on how "mm" vs. "active_mm" in
+> the task_struct are supposed to be used?  (My apologies if this was
+> discussed on the mailing lists---I just returned from vacation and
+> wasn't able to follow linux-kernel for a while).
+
+Basically, the new setup is:
+
+ - we have "real address spaces" and "anonymous address spaces". The
+   difference is that an anonymous address space doesn't care about the
+   user-level page tables at all, so when we do a context switch into an
+   anonymous address space we just leave the previous address space
+   active.
+
+   The obvious use for a "anonymous address space" is any thread that
+   doesn't need any user mappings - all kernel threads basically fall into
+   this category, but even "real" threads can temporarily say that for
+   some amount of time they are not going to be interested in user space,
+   and that the scheduler might as well try to avoid wasting time on
+   switching the VM state around. Currently only the old-style bdflush
+   sync does that.
+
+ - "tsk->mm" points to the "real address space". For an anonymous process,
+   tsk->mm will be NULL, for the logical reason that an anonymous process
+   really doesn't _have_ a real address space at all.
+
+ - however, we obviously need to keep track of which address space we
+   "stole" for such an anonymous user. For that, we have "tsk->active_mm",
+   which shows what the currently active address space is.
+
+   The rule is that for a process with a real address space (ie tsk->mm is
+   non-NULL) the active_mm obviously always has to be the same as the real
+   one.
+
+   For a anonymous process, tsk->mm == NULL, and tsk->active_mm is the
+   "borrowed" mm while the anonymous process is running. When the
+   anonymous process gets scheduled away, the borrowed address space is
+   returned and cleared.
+
+To support all that, the "struct mm_struct" now has two counters: a
+"mm_users" counter that is how many "real address space users" there are,
+and a "mm_count" counter that is the number of "lazy" users (ie anonymous
+users) plus one if there are any real users.
+
+Usually there is at least one real user, but it could be that the real
+user exited on another CPU while a lazy user was still active, so you do
+actually get cases where you have a address space that is _only_ used by
+lazy users. That is often a short-lived state, because once that thread
+gets scheduled away in favour of a real thread, the "zombie" mm gets
+released because "mm_users" becomes zero.
+
+Also, a new rule is that _nobody_ ever has "init_mm" as a real MM any
+more. "init_mm" should be considered just a "lazy context when no other
+context is available", and in fact it is mainly used just at bootup when
+no real VM has yet been created. So code that used to check
+
+	if (current->mm == &init_mm)
+
+should generally just do
+
+	if (!current->mm)
+
+instead (which makes more sense anyway - the test is basically one of "do
+we have a user context", and is generally done by the page fault handler
+and things like that).
+
+Anyway, I put a pre-patch-2.3.13-1 on ftp.kernel.org just a moment ago,
+because it slightly changes the interfaces to accomodate the alpha (who
+would have thought it, but the alpha actually ends up having one of the
+ugliest context switch codes - unlike the other architectures where the MM
+and register state is separate, the alpha PALcode joins the two, and you
+need to switch both together).
+
+(From http://marc.info/?l=linux-kernel&m=93337278602211&w=2)
diff --git a/Documentation/vm/unevictable-lru.txt b/Documentation/vm/unevictable-lru.txt
index 0706a72..2d70d0d 100644
--- a/Documentation/vm/unevictable-lru.txt
+++ b/Documentation/vm/unevictable-lru.txt
@@ -1,588 +1,691 @@
-
-This document describes the Linux memory management "Unevictable LRU"
-infrastructure and the use of this infrastructure to manage several types
-of "unevictable" pages.  The document attempts to provide the overall
-rationale behind this mechanism and the rationale for some of the design
-decisions that drove the implementation.  The latter design rationale is
-discussed in the context of an implementation description.  Admittedly, one
-can obtain the implementation details--the "what does it do?"--by reading the
-code.  One hopes that the descriptions below add value by provide the answer
-to "why does it do that?".
-
-Unevictable LRU Infrastructure:
-
-The Unevictable LRU adds an additional LRU list to track unevictable pages
-and to hide these pages from vmscan.  This mechanism is based on a patch by
-Larry Woodman of Red Hat to address several scalability problems with page
+			==============================
+			UNEVICTABLE LRU INFRASTRUCTURE
+			==============================
+
+========
+CONTENTS
+========
+
+ (*) The Unevictable LRU
+
+     - The unevictable page list.
+     - Memory control group interaction.
+     - Marking address spaces unevictable.
+     - Detecting Unevictable Pages.
+     - vmscan's handling of unevictable pages.
+
+ (*) mlock()'d pages.
+
+     - History.
+     - Basic management.
+     - mlock()/mlockall() system call handling.
+     - Filtering special vmas.
+     - munlock()/munlockall() system call handling.
+     - Migrating mlocked pages.
+     - mmap(MAP_LOCKED) system call handling.
+     - munmap()/exit()/exec() system call handling.
+     - try_to_unmap().
+     - try_to_munlock() reverse map scan.
+     - Page reclaim in shrink_*_list().
+
+
+============
+INTRODUCTION
+============
+
+This document describes the Linux memory manager's "Unevictable LRU"
+infrastructure and the use of this to manage several types of "unevictable"
+pages.
+
+The document attempts to provide the overall rationale behind this mechanism
+and the rationale for some of the design decisions that drove the
+implementation.  The latter design rationale is discussed in the context of an
+implementation description.  Admittedly, one can obtain the implementation
+details - the "what does it do?" - by reading the code.  One hopes that the
+descriptions below add value by provide the answer to "why does it do that?".
+
+
+===================
+THE UNEVICTABLE LRU
+===================
+
+The Unevictable LRU facility adds an additional LRU list to track unevictable
+pages and to hide these pages from vmscan.  This mechanism is based on a patch
+by Larry Woodman of Red Hat to address several scalability problems with page
 reclaim in Linux.  The problems have been observed at customer sites on large
-memory x86_64 systems.  For example, a non-numal x86_64 platform with 128GB
-of main memory will have over 32 million 4k pages in a single zone.  When a
-large fraction of these pages are not evictable for any reason [see below],
-vmscan will spend a lot of time scanning the LRU lists looking for the small
-fraction of pages that are evictable.  This can result in a situation where
-all cpus are spending 100% of their time in vmscan for hours or days on end,
-with the system completely unresponsive.
-
-The Unevictable LRU infrastructure addresses the following classes of
-unevictable pages:
-
-+ page owned by ramfs
-+ page mapped into SHM_LOCKed shared memory regions
-+ page mapped into VM_LOCKED [mlock()ed] vmas
-
-The infrastructure might be able to handle other conditions that make pages
+memory x86_64 systems.
+
+To illustrate this with an example, a non-NUMA x86_64 platform with 128GB of
+main memory will have over 32 million 4k pages in a single zone.  When a large
+fraction of these pages are not evictable for any reason [see below], vmscan
+will spend a lot of time scanning the LRU lists looking for the small fraction
+of pages that are evictable.  This can result in a situation where all CPUs are
+spending 100% of their time in vmscan for hours or days on end, with the system
+completely unresponsive.
+
+The unevictable list addresses the following classes of unevictable pages:
+
+ (*) Those owned by ramfs.
+
+ (*) Those mapped into SHM_LOCK'd shared memory regions.
+
+ (*) Those mapped into VM_LOCKED [mlock()ed] VMAs.
+
+The infrastructure may also be able to handle other conditions that make pages
 unevictable, either by definition or by circumstance, in the future.
 
 
-The Unevictable LRU List
+THE UNEVICTABLE PAGE LIST
+-------------------------
 
 The Unevictable LRU infrastructure consists of an additional, per-zone, LRU list
 called the "unevictable" list and an associated page flag, PG_unevictable, to
-indicate that the page is being managed on the unevictable list.  The
-PG_unevictable flag is analogous to, and mutually exclusive with, the PG_active
-flag in that it indicates on which LRU list a page resides when PG_lru is set.
-The unevictable LRU list is source configurable based on the UNEVICTABLE_LRU
-Kconfig option.
+indicate that the page is being managed on the unevictable list.
+
+The PG_unevictable flag is analogous to, and mutually exclusive with, the
+PG_active flag in that it indicates on which LRU list a page resides when
+PG_lru is set.  The unevictable list is compile-time configurable based on the
+UNEVICTABLE_LRU Kconfig option.
 
 The Unevictable LRU infrastructure maintains unevictable pages on an additional
 LRU list for a few reasons:
 
-1) We get to "treat unevictable pages just like we treat other pages in the
-   system, which means we get to use the same code to manipulate them, the
-   same code to isolate them (for migrate, etc.), the same code to keep track
-   of the statistics, etc..." [Rik van Riel]
+ (1) We get to "treat unevictable pages just like we treat other pages in the
+     system - which means we get to use the same code to manipulate them, the
+     same code to isolate them (for migrate, etc.), the same code to keep track
+     of the statistics, etc..." [Rik van Riel]
+
+ (2) We want to be able to migrate unevictable pages between nodes for memory
+     defragmentation, workload management and memory hotplug.  The linux kernel
+     can only migrate pages that it can successfully isolate from the LRU
+     lists.  If we were to maintain pages elsewhere than on an LRU-like list,
+     where they can be found by isolate_lru_page(), we would prevent their
+     migration, unless we reworked migration code to find the unevictable pages
+     itself.
 
-2) We want to be able to migrate unevictable pages between nodes--for memory
-   defragmentation, workload management and memory hotplug.  The linux kernel
-   can only migrate pages that it can successfully isolate from the lru lists.
-   If we were to maintain pages elsewise than on an lru-like list, where they
-   can be found by isolate_lru_page(), we would prevent their migration, unless
-   we reworked migration code to find the unevictable pages.
 
+The unevictable list does not differentiate between file-backed and anonymous,
+swap-backed pages.  This differentiation is only important while the pages are,
+in fact, evictable.
 
-The unevictable LRU list does not differentiate between file backed and swap
-backed [anon] pages.  This differentiation is only important while the pages
-are, in fact, evictable.
+The unevictable list benefits from the "arrayification" of the per-zone LRU
+lists and statistics originally proposed and posted by Christoph Lameter.
 
-The unevictable LRU list benefits from the "arrayification" of the per-zone
-LRU lists and statistics originally proposed and posted by Christoph Lameter.
+The unevictable list does not use the LRU pagevec mechanism. Rather,
+unevictable pages are placed directly on the page's zone's unevictable list
+under the zone lru_lock.  This allows us to prevent the stranding of pages on
+the unevictable list when one task has the page isolated from the LRU and other
+tasks are changing the "evictability" state of the page.
 
-The unevictable list does not use the lru pagevec mechanism. Rather,
-unevictable pages are placed directly on the page's zone's unevictable
-list under the zone lru_lock.  The reason for this is to prevent stranding
-of pages on the unevictable list when one task has the page isolated from the
-lru and other tasks are changing the "evictability" state of the page.
 
+MEMORY CONTROL GROUP INTERACTION
+--------------------------------
 
-Unevictable LRU and Memory Controller Interaction
+The unevictable LRU facility interacts with the memory control group [aka
+memory controller; see Documentation/cgroups/memory.txt] by extending the
+lru_list enum.
+
+The memory controller data structure automatically gets a per-zone unevictable
+list as a result of the "arrayification" of the per-zone LRU lists (one per
+lru_list enum element).  The memory controller tracks the movement of pages to
+and from the unevictable list.
 
-The memory controller data structure automatically gets a per zone unevictable
-lru list as a result of the "arrayification" of the per-zone LRU lists.  The
-memory controller tracks the movement of pages to and from the unevictable list.
 When a memory control group comes under memory pressure, the controller will
 not attempt to reclaim pages on the unevictable list.  This has a couple of
-effects.  Because the pages are "hidden" from reclaim on the unevictable list,
-the reclaim process can be more efficient, dealing only with pages that have
-a chance of being reclaimed.  On the other hand, if too many of the pages
-charged to the control group are unevictable, the evictable portion of the
-working set of the tasks in the control group may not fit into the available
-memory.  This can cause the control group to thrash or to oom-kill tasks.
-
-
-Unevictable LRU:  Detecting Unevictable Pages
-
-The function page_evictable(page, vma) in vmscan.c determines whether a
-page is evictable or not.  For ramfs pages and pages in SHM_LOCKed regions,
-page_evictable() tests a new address space flag, AS_UNEVICTABLE, in the page's
-address space using a wrapper function.  Wrapper functions are used to set,
-clear and test the flag to reduce the requirement for #ifdef's throughout the
-source code.  AS_UNEVICTABLE is set on ramfs inode/mapping when it is created.
-This flag remains for the life of the inode.
-
-For shared memory regions, AS_UNEVICTABLE is set when an application
-successfully SHM_LOCKs the region and is removed when the region is
-SHM_UNLOCKed.  Note that shmctl(SHM_LOCK, ...) does not populate the page
-tables for the region as does, for example, mlock().   So, we make no special
-effort to push any pages in the SHM_LOCKed region to the unevictable list.
-Vmscan will do this when/if it encounters the pages during reclaim.  On
-SHM_UNLOCK, shmctl() scans the pages in the region and "rescues" them from the
-unevictable list if no other condition keeps them unevictable.  If a SHM_LOCKed
-region is destroyed, the pages are also "rescued" from the unevictable list in
-the process of freeing them.
-
-page_evictable() detects mlock()ed pages by testing an additional page flag,
-PG_mlocked via the PageMlocked() wrapper.  If the page is NOT mlocked, and a
-non-NULL vma is supplied, page_evictable() will check whether the vma is
+effects:
+
+ (1) Because the pages are "hidden" from reclaim on the unevictable list, the
+     reclaim process can be more efficient, dealing only with pages that have a
+     chance of being reclaimed.
+
+ (2) On the other hand, if too many of the pages charged to the control group
+     are unevictable, the evictable portion of the working set of the tasks in
+     the control group may not fit into the available memory.  This can cause
+     the control group to thrash or to OOM-kill tasks.
+
+
+MARKING ADDRESS SPACES UNEVICTABLE
+----------------------------------
+
+For facilities such as ramfs none of the pages attached to the address space
+may be evicted.  To prevent eviction of any such pages, the AS_UNEVICTABLE
+address space flag is provided, and this can be manipulated by a filesystem
+using a number of wrapper functions:
+
+ (*) void mapping_set_unevictable(struct address_space *mapping);
+
+	Mark the address space as being completely unevictable.
+
+ (*) void mapping_clear_unevictable(struct address_space *mapping);
+
+	Mark the address space as being evictable.
+
+ (*) int mapping_unevictable(struct address_space *mapping);
+
+	Query the address space, and return true if it is completely
+	unevictable.
+
+These are currently used in two places in the kernel:
+
+ (1) By ramfs to mark the address spaces of its inodes when they are created,
+     and this mark remains for the life of the inode.
+
+ (2) By SYSV SHM to mark SHM_LOCK'd address spaces until SHM_UNLOCK is called.
+
+     Note that SHM_LOCK is not required to page in the locked pages if they're
+     swapped out; the application must touch the pages manually if it wants to
+     ensure they're in memory.
+
+
+DETECTING UNEVICTABLE PAGES
+---------------------------
+
+The function page_evictable() in vmscan.c determines whether a page is
+evictable or not using the query function outlined above [see section "Marking
+address spaces unevictable"] to check the AS_UNEVICTABLE flag.
+
+For address spaces that are so marked after being populated (as SHM regions
+might be), the lock action (eg: SHM_LOCK) can be lazy, and need not populate
+the page tables for the region as does, for example, mlock(), nor need it make
+any special effort to push any pages in the SHM_LOCK'd area to the unevictable
+list.  Instead, vmscan will do this if and when it encounters the pages during
+a reclamation scan.
+
+On an unlock action (such as SHM_UNLOCK), the unlocker (eg: shmctl()) must scan
+the pages in the region and "rescue" them from the unevictable list if no other
+condition is keeping them unevictable.  If an unevictable region is destroyed,
+the pages are also "rescued" from the unevictable list in the process of
+freeing them.
+
+page_evictable() also checks for mlocked pages by testing an additional page
+flag, PG_mlocked (as wrapped by PageMlocked()).  If the page is NOT mlocked,
+and a non-NULL VMA is supplied, page_evictable() will check whether the VMA is
 VM_LOCKED via is_mlocked_vma().  is_mlocked_vma() will SetPageMlocked() and
 update the appropriate statistics if the vma is VM_LOCKED.  This method allows
 efficient "culling" of pages in the fault path that are being faulted in to
-VM_LOCKED vmas.
+VM_LOCKED VMAs.
 
 
-Unevictable Pages and Vmscan [shrink_*_list()]
+VMSCAN'S HANDLING OF UNEVICTABLE PAGES
+--------------------------------------
 
 If unevictable pages are culled in the fault path, or moved to the unevictable
-list at mlock() or mmap() time, vmscan will never encounter the pages until
-they have become evictable again, for example, via munlock() and have been
-"rescued" from the unevictable list.  However, there may be situations where we
-decide, for the sake of expediency, to leave a unevictable page on one of the
-regular active/inactive LRU lists for vmscan to deal with.  Vmscan checks for
-such pages in all of the shrink_{active|inactive|page}_list() functions and
-will "cull" such pages that it encounters--that is, it diverts those pages to
-the unevictable list for the zone being scanned.
-
-There may be situations where a page is mapped into a VM_LOCKED vma, but the
-page is not marked as PageMlocked.  Such pages will make it all the way to
+list at mlock() or mmap() time, vmscan will not encounter the pages until they
+have become evictable again (via munlock() for example) and have been "rescued"
+from the unevictable list.  However, there may be situations where we decide,
+for the sake of expediency, to leave a unevictable page on one of the regular
+active/inactive LRU lists for vmscan to deal with.  vmscan checks for such
+pages in all of the shrink_{active|inactive|page}_list() functions and will
+"cull" such pages that it encounters: that is, it diverts those pages to the
+unevictable list for the zone being scanned.
+
+There may be situations where a page is mapped into a VM_LOCKED VMA, but the
+page is not marked as PG_mlocked.  Such pages will make it all the way to
 shrink_page_list() where they will be detected when vmscan walks the reverse
-map in try_to_unmap().  If try_to_unmap() returns SWAP_MLOCK, shrink_page_list()
-will cull the page at that point.
+map in try_to_unmap().  If try_to_unmap() returns SWAP_MLOCK,
+shrink_page_list() will cull the page at that point.
 
-To "cull" an unevictable page, vmscan simply puts the page back on the lru
-list using putback_lru_page()--the inverse operation to isolate_lru_page()--
-after dropping the page lock.  Because the condition which makes the page
-unevictable may change once the page is unlocked, putback_lru_page() will
-recheck the unevictable state of a page that it places on the unevictable lru
-list.  If the page has become unevictable, putback_lru_page() removes it from
-the list and retries, including the page_unevictable() test.  Because such a
-race is a rare event and movement of pages onto the unevictable list should be
-rare, these extra evictabilty checks should not occur in the majority of calls
-to putback_lru_page().
+To "cull" an unevictable page, vmscan simply puts the page back on the LRU list
+using putback_lru_page() - the inverse operation to isolate_lru_page() - after
+dropping the page lock.  Because the condition which makes the page unevictable
+may change once the page is unlocked, putback_lru_page() will recheck the
+unevictable state of a page that it places on the unevictable list.  If the
+page has become unevictable, putback_lru_page() removes it from the list and
+retries, including the page_unevictable() test.  Because such a race is a rare
+event and movement of pages onto the unevictable list should be rare, these
+extra evictabilty checks should not occur in the majority of calls to
+putback_lru_page().
 
 
-Mlocked Page:  Prior Work
+=============
+MLOCKED PAGES
+=============
 
-The "Unevictable Mlocked Pages" infrastructure is based on work originally
+The unevictable page list is also useful for mlock(), in addition to ramfs and
+SYSV SHM.  Note that mlock() is only available in CONFIG_MMU=y situations; in
+NOMMU situations, all mappings are effectively mlocked.
+
+
+HISTORY
+-------
+
+The "Unevictable mlocked Pages" infrastructure is based on work originally
 posted by Nick Piggin in an RFC patch entitled "mm: mlocked pages off LRU".
-Nick posted his patch as an alternative to a patch posted by Christoph
-Lameter to achieve the same objective--hiding mlocked pages from vmscan.
-In Nick's patch, he used one of the struct page lru list link fields as a count
-of VM_LOCKED vmas that map the page.  This use of the link field for a count
-prevented the management of the pages on an LRU list.  Thus, mlocked pages were
-not migratable as isolate_lru_page() could not find them and the lru list link
-field was not available to the migration subsystem.  Nick resolved this by
-putting mlocked pages back on the lru list before attempting to isolate them,
-thus abandoning the count of VM_LOCKED vmas.  When Nick's patch was integrated
-with the Unevictable LRU work, the count was replaced by walking the reverse
-map to determine whether any VM_LOCKED vmas mapped the page.  More on this
-below.
-
-
-Mlocked Pages:  Basic Management
-
-Mlocked pages--pages mapped into a VM_LOCKED vma--represent one class of
-unevictable pages.  When such a page has been "noticed" by the memory
-management subsystem, the page is marked with the PG_mlocked [PageMlocked()]
-flag.  A PageMlocked() page will be placed on the unevictable LRU list when
-it is added to the LRU.   Pages can be "noticed" by memory management in
-several places:
-
-1) in the mlock()/mlockall() system call handlers.
-2) in the mmap() system call handler when mmap()ing a region with the
-   MAP_LOCKED flag, or mmap()ing a region in a task that has called
-   mlockall() with the MCL_FUTURE flag.  Both of these conditions result
-   in the VM_LOCKED flag being set for the vma.
-3) in the fault path, if mlocked pages are "culled" in the fault path,
-   and when a VM_LOCKED stack segment is expanded.
-4) as mentioned above, in vmscan:shrink_page_list() when attempting to
-   reclaim a page in a VM_LOCKED vma via try_to_unmap().
-
-Mlocked pages become unlocked and rescued from the unevictable list when:
-
-1) mapped in a range unlocked via the munlock()/munlockall() system calls.
-2) munmapped() out of the last VM_LOCKED vma that maps the page, including
-   unmapping at task exit.
-3) when the page is truncated from the last VM_LOCKED vma of an mmap()ed file.
-4) before a page is COWed in a VM_LOCKED vma.
-
-
-Mlocked Pages:  mlock()/mlockall() System Call Handling
+Nick posted his patch as an alternative to a patch posted by Christoph Lameter
+to achieve the same objective: hiding mlocked pages from vmscan.
+
+In Nick's patch, he used one of the struct page LRU list link fields as a count
+of VM_LOCKED VMAs that map the page.  This use of the link field for a count
+prevented the management of the pages on an LRU list, and thus mlocked pages
+were not migratable as isolate_lru_page() could not find them, and the LRU list
+link field was not available to the migration subsystem.
+
+Nick resolved this by putting mlocked pages back on the lru list before
+attempting to isolate them, thus abandoning the count of VM_LOCKED VMAs.  When
+Nick's patch was integrated with the Unevictable LRU work, the count was
+replaced by walking the reverse map to determine whether any VM_LOCKED VMAs
+mapped the page.  More on this below.
+
+
+BASIC MANAGEMENT
+----------------
+
+mlocked pages - pages mapped into a VM_LOCKED VMA - are a class of unevictable
+pages.  When such a page has been "noticed" by the memory management subsystem,
+the page is marked with the PG_mlocked flag.  This can be manipulated using the
+PageMlocked() functions.
+
+A PG_mlocked page will be placed on the unevictable list when it is added to
+the LRU.  Such pages can be "noticed" by memory management in several places:
+
+ (1) in the mlock()/mlockall() system call handlers;
+
+ (2) in the mmap() system call handler when mmapping a region with the
+     MAP_LOCKED flag;
+
+ (3) mmapping a region in a task that has called mlockall() with the MCL_FUTURE
+     flag
+
+ (4) in the fault path, if mlocked pages are "culled" in the fault path,
+     and when a VM_LOCKED stack segment is expanded; or
+
+ (5) as mentioned above, in vmscan:shrink_page_list() when attempting to
+     reclaim a page in a VM_LOCKED VMA via try_to_unmap()
+
+all of which result in the VM_LOCKED flag being set for the VMA if it doesn't
+already have it set.
+
+mlocked pages become unlocked and rescued from the unevictable list when:
+
+ (1) mapped in a range unlocked via the munlock()/munlockall() system calls;
+
+ (2) munmap()'d out of the last VM_LOCKED VMA that maps the page, including
+     unmapping at task exit;
+
+ (3) when the page is truncated from the last VM_LOCKED VMA of an mmapped file;
+     or
+
+ (4) before a page is COW'd in a VM_LOCKED VMA.
+
+
+mlock()/mlockall() SYSTEM CALL HANDLING
+---------------------------------------
 
 Both [do_]mlock() and [do_]mlockall() system call handlers call mlock_fixup()
-for each vma in the range specified by the call.  In the case of mlockall(),
+for each VMA in the range specified by the call.  In the case of mlockall(),
 this is the entire active address space of the task.  Note that mlock_fixup()
-is used for both mlock()ing and munlock()ing a range of memory.  A call to
-mlock() an already VM_LOCKED vma, or to munlock() a vma that is not VM_LOCKED
-is treated as a no-op--mlock_fixup() simply returns.
-
-If the vma passes some filtering described in "Mlocked Pages:  Filtering Vmas"
-below, mlock_fixup() will attempt to merge the vma with its neighbors or split
-off a subset of the vma if the range does not cover the entire vma.  Once the
-vma has been merged or split or neither, mlock_fixup() will call
-__mlock_vma_pages_range() to fault in the pages via get_user_pages() and
-to mark the pages as mlocked via mlock_vma_page().
-
-Note that the vma being mlocked might be mapped with PROT_NONE.  In this case,
-get_user_pages() will be unable to fault in the pages.  That's OK.  If pages
-do end up getting faulted into this VM_LOCKED vma, we'll handle them in the
+is used for both mlocking and munlocking a range of memory.  A call to mlock()
+an already VM_LOCKED VMA, or to munlock() a VMA that is not VM_LOCKED is
+treated as a no-op, and mlock_fixup() simply returns.
+
+If the VMA passes some filtering as described in "Filtering Special Vmas"
+below, mlock_fixup() will attempt to merge the VMA with its neighbors or split
+off a subset of the VMA if the range does not cover the entire VMA.  Once the
+VMA has been merged or split or neither, mlock_fixup() will call
+__mlock_vma_pages_range() to fault in the pages via get_user_pages() and to
+mark the pages as mlocked via mlock_vma_page().
+
+Note that the VMA being mlocked might be mapped with PROT_NONE.  In this case,
+get_user_pages() will be unable to fault in the pages.  That's okay.  If pages
+do end up getting faulted into this VM_LOCKED VMA, we'll handle them in the
 fault path or in vmscan.
 
 Also note that a page returned by get_user_pages() could be truncated or
-migrated out from under us, while we're trying to mlock it.  To detect
-this, __mlock_vma_pages_range() tests the page_mapping after acquiring
-the page lock.  If the page is still associated with its mapping, we'll
-go ahead and call mlock_vma_page().  If the mapping is gone, we just
-unlock the page and move on.  Worse case, this results in page mapped
-in a VM_LOCKED vma remaining on a normal LRU list without being
-PageMlocked().  Again, vmscan will detect and cull such pages.
-
-mlock_vma_page(), called with the page locked [N.B., not "mlocked"], will
-TestSetPageMlocked() for each page returned by get_user_pages().  We use
-TestSetPageMlocked() because the page might already be mlocked by another
-task/vma and we don't want to do extra work.  We especially do not want to
-count an mlocked page more than once in the statistics.  If the page was
-already mlocked, mlock_vma_page() is done.
+migrated out from under us, while we're trying to mlock it.  To detect this,
+__mlock_vma_pages_range() checks page_mapping() after acquiring the page lock.
+If the page is still associated with its mapping, we'll go ahead and call
+mlock_vma_page().  If the mapping is gone, we just unlock the page and move on.
+In the worst case, this will result in a page mapped in a VM_LOCKED VMA
+remaining on a normal LRU list without being PageMlocked().  Again, vmscan will
+detect and cull such pages.
+
+mlock_vma_page() will call TestSetPageMlocked() for each page returned by
+get_user_pages().  We use TestSetPageMlocked() because the page might already
+be mlocked by another task/VMA and we don't want to do extra work.  We
+especially do not want to count an mlocked page more than once in the
+statistics.  If the page was already mlocked, mlock_vma_page() need do nothing
+more.
 
 If the page was NOT already mlocked, mlock_vma_page() attempts to isolate the
 page from the LRU, as it is likely on the appropriate active or inactive list
-at that time.  If the isolate_lru_page() succeeds, mlock_vma_page() will
-putback the page--putback_lru_page()--which will notice that the page is now
-mlocked and divert the page to the zone's unevictable LRU list.  If
+at that time.  If the isolate_lru_page() succeeds, mlock_vma_page() will put
+back the page - by calling putback_lru_page() - which will notice that the page
+is now mlocked and divert the page to the zone's unevictable list.  If
 mlock_vma_page() is unable to isolate the page from the LRU, vmscan will handle
-it later if/when it attempts to reclaim the page.
+it later if and when it attempts to reclaim the page.
 
 
-Mlocked Pages:  Filtering Special Vmas
+FILTERING SPECIAL VMAS
+----------------------
 
-mlock_fixup() filters several classes of "special" vmas:
+mlock_fixup() filters several classes of "special" VMAs:
 
-1) vmas with VM_IO|VM_PFNMAP set are skipped entirely.  The pages behind
+1) VMAs with VM_IO or VM_PFNMAP set are skipped entirely.  The pages behind
    these mappings are inherently pinned, so we don't need to mark them as
-   mlocked.  In any case, most of the pages have no struct page in which to
-   so mark the page.  Because of this, get_user_pages() will fail for these
-   vmas, so there is no sense in attempting to visit them.
-
-2) vmas mapping hugetlbfs page are already effectively pinned into memory.
-   We don't need nor want to mlock() these pages.  However, to preserve the
-   prior behavior of mlock()--before the unevictable/mlock changes--
-   mlock_fixup() will call make_pages_present() in the hugetlbfs vma range
-   to allocate the huge pages and populate the ptes.
-
-3) vmas with VM_DONTEXPAND|VM_RESERVED are generally user space mappings of
-   kernel pages, such as the vdso page, relay channel pages, etc.  These pages
+   mlocked.  In any case, most of the pages have no struct page in which to so
+   mark the page.  Because of this, get_user_pages() will fail for these VMAs,
+   so there is no sense in attempting to visit them.
+
+2) VMAs mapping hugetlbfs page are already effectively pinned into memory.  We
+   neither need nor want to mlock() these pages.  However, to preserve the
+   prior behavior of mlock() - before the unevictable/mlock changes -
+   mlock_fixup() will call make_pages_present() in the hugetlbfs VMA range to
+   allocate the huge pages and populate the ptes.
+
+3) VMAs with VM_DONTEXPAND or VM_RESERVED are generally userspace mappings of
+   kernel pages, such as the VDSO page, relay channel pages, etc.  These pages
    are inherently unevictable and are not managed on the LRU lists.
-   mlock_fixup() treats these vmas the same as hugetlbfs vmas.  It calls
+   mlock_fixup() treats these VMAs the same as hugetlbfs VMAs.  It calls
    make_pages_present() to populate the ptes.
 
-Note that for all of these special vmas, mlock_fixup() does not set the
+Note that for all of these special VMAs, mlock_fixup() does not set the
 VM_LOCKED flag.  Therefore, we won't have to deal with them later during
-munlock() or munmap()--for example, at task exit.  Neither does mlock_fixup()
-account these vmas against the task's "locked_vm".
-
-Mlocked Pages:  Downgrading the Mmap Semaphore.
-
-mlock_fixup() must be called with the mmap semaphore held for write, because
-it may have to merge or split vmas.  However, mlocking a large region of
-memory can take a long time--especially if vmscan must reclaim pages to
-satisfy the regions requirements.  Faulting in a large region with the mmap
-semaphore held for write can hold off other faults on the address space, in
-the case of a multi-threaded task.  It can also hold off scans of the task's
-address space via /proc.  While testing under heavy load, it was observed that
-the ps(1) command could be held off for many minutes while a large segment was
-mlock()ed down.
-
-To address this issue, and to make the system more responsive during mlock()ing
-of large segments, mlock_fixup() downgrades the mmap semaphore to read mode
-during the call to __mlock_vma_pages_range().  This works fine.  However, the
-callers of mlock_fixup() expect the semaphore to be returned in write mode.
-So, mlock_fixup() "upgrades" the semphore to write mode.  Linux does not
-support an atomic upgrade_sem() call, so mlock_fixup() must drop the semaphore
-and reacquire it in write mode.  In a multi-threaded task, it is possible for
-the task memory map to change while the semaphore is dropped.  Therefore,
-mlock_fixup() looks up the vma at the range start address after reacquiring
-the semaphore in write mode and verifies that it still covers the original
-range.  If not, mlock_fixup() returns an error [-EAGAIN].  All callers of
-mlock_fixup() have been changed to deal with this new error condition.
-
-Note:  when munlocking a region, all of the pages should already be resident--
-unless we have racing threads mlocking() and munlocking() regions.  So,
-unlocking should not have to wait for page allocations nor faults  of any kind.
-Therefore mlock_fixup() does not downgrade the semaphore for munlock().
-
-
-Mlocked Pages:  munlock()/munlockall() System Call Handling
-
-The munlock() and munlockall() system calls are handled by the same functions--
-do_mlock[all]()--as the mlock() and mlockall() system calls with the unlock
-vs lock operation indicated by an argument.  So, these system calls are also
-handled by mlock_fixup().  Again, if called for an already munlock()ed vma,
-mlock_fixup() simply returns.  Because of the vma filtering discussed above,
-VM_LOCKED will not be set in any "special" vmas.  So, these vmas will be
+munlock(), munmap() or task exit.  Neither does mlock_fixup() account these
+VMAs against the task's "locked_vm".
+
+
+munlock()/munlockall() SYSTEM CALL HANDLING
+-------------------------------------------
+
+The munlock() and munlockall() system calls are handled by the same functions -
+do_mlock[all]() - as the mlock() and mlockall() system calls with the unlock vs
+lock operation indicated by an argument.  So, these system calls are also
+handled by mlock_fixup().  Again, if called for an already munlocked VMA,
+mlock_fixup() simply returns.  Because of the VMA filtering discussed above,
+VM_LOCKED will not be set in any "special" VMAs.  So, these VMAs will be
 ignored for munlock.
 
-If the vma is VM_LOCKED, mlock_fixup() again attempts to merge or split off
-the specified range.  The range is then munlocked via the function
-__mlock_vma_pages_range()--the same function used to mlock a vma range--
+If the VMA is VM_LOCKED, mlock_fixup() again attempts to merge or split off the
+specified range.  The range is then munlocked via the function
+__mlock_vma_pages_range() - the same function used to mlock a VMA range -
 passing a flag to indicate that munlock() is being performed.
 
-Because the vma access protections could have been changed to PROT_NONE after
+Because the VMA access protections could have been changed to PROT_NONE after
 faulting in and mlocking pages, get_user_pages() was unreliable for visiting
-these pages for munlocking.  Because we don't want to leave pages mlocked(),
+these pages for munlocking.  Because we don't want to leave pages mlocked,
 get_user_pages() was enhanced to accept a flag to ignore the permissions when
-fetching the pages--all of which should be resident as a result of previous
-mlock()ing.
+fetching the pages - all of which should be resident as a result of previous
+mlocking.
 
 For munlock(), __mlock_vma_pages_range() unlocks individual pages by calling
 munlock_vma_page().  munlock_vma_page() unconditionally clears the PG_mlocked
-flag using TestClearPageMlocked().  As with mlock_vma_page(), munlock_vma_page()
-use the Test*PageMlocked() function to handle the case where the page might
-have already been unlocked by another task.  If the page was mlocked,
-munlock_vma_page() updates that zone statistics for the number of mlocked
-pages.  Note, however, that at this point we haven't checked whether the page
-is mapped by other VM_LOCKED vmas.
-
-We can't call try_to_munlock(), the function that walks the reverse map to check
-for other VM_LOCKED vmas, without first isolating the page from the LRU.
+flag using TestClearPageMlocked().  As with mlock_vma_page(),
+munlock_vma_page() use the Test*PageMlocked() function to handle the case where
+the page might have already been unlocked by another task.  If the page was
+mlocked, munlock_vma_page() updates that zone statistics for the number of
+mlocked pages.  Note, however, that at this point we haven't checked whether
+the page is mapped by other VM_LOCKED VMAs.
+
+We can't call try_to_munlock(), the function that walks the reverse map to
+check for other VM_LOCKED VMAs, without first isolating the page from the LRU.
 try_to_munlock() is a variant of try_to_unmap() and thus requires that the page
-not be on an lru list.  [More on these below.]  However, the call to
-isolate_lru_page() could fail, in which case we couldn't try_to_munlock().
-So, we go ahead and clear PG_mlocked up front, as this might be the only chance
-we have.  If we can successfully isolate the page, we go ahead and
+not be on an LRU list [more on these below].  However, the call to
+isolate_lru_page() could fail, in which case we couldn't try_to_munlock().  So,
+we go ahead and clear PG_mlocked up front, as this might be the only chance we
+have.  If we can successfully isolate the page, we go ahead and
 try_to_munlock(), which will restore the PG_mlocked flag and update the zone
-page statistics if it finds another vma holding the page mlocked.  If we fail
+page statistics if it finds another VMA holding the page mlocked.  If we fail
 to isolate the page, we'll have left a potentially mlocked page on the LRU.
-This is fine, because we'll catch it later when/if vmscan tries to reclaim the
-page.  This should be relatively rare.
-
-Mlocked Pages:  Migrating Them...
-
-A page that is being migrated has been isolated from the lru lists and is
-held locked across unmapping of the page, updating the page's mapping
-[address_space] entry and copying the contents and state, until the
-page table entry has been replaced with an entry that refers to the new
-page.  Linux supports migration of mlocked pages and other unevictable
-pages.  This involves simply moving the PageMlocked and PageUnevictable states
-from the old page to the new page.
-
-Note that page migration can race with mlocking or munlocking of the same
-page.  This has been discussed from the mlock/munlock perspective in the
-respective sections above.  Both processes [migration, m[un]locking], hold
-the page locked.  This provides the first level of synchronization.  Page
-migration zeros out the page_mapping of the old page before unlocking it,
-so m[un]lock can skip these pages by testing the page mapping under page
-lock.
-
-When completing page migration, we place the new and old pages back onto the
-lru after dropping the page lock.  The "unneeded" page--old page on success,
-new page on failure--will be freed when the reference count held by the
-migration process is released.  To ensure that we don't strand pages on the
-unevictable list because of a race between munlock and migration, page
-migration uses the putback_lru_page() function to add migrated pages back to
-the lru.
-
-
-Mlocked Pages:  mmap(MAP_LOCKED) System Call Handling
+This is fine, because we'll catch it later if and if vmscan tries to reclaim
+the page.  This should be relatively rare.
+
+
+MIGRATING MLOCKED PAGES
+-----------------------
+
+A page that is being migrated has been isolated from the LRU lists and is held
+locked across unmapping of the page, updating the page's address space entry
+and copying the contents and state, until the page table entry has been
+replaced with an entry that refers to the new page.  Linux supports migration
+of mlocked pages and other unevictable pages.  This involves simply moving the
+PG_mlocked and PG_unevictable states from the old page to the new page.
+
+Note that page migration can race with mlocking or munlocking of the same page.
+This has been discussed from the mlock/munlock perspective in the respective
+sections above.  Both processes (migration and m[un]locking) hold the page
+locked.  This provides the first level of synchronization.  Page migration
+zeros out the page_mapping of the old page before unlocking it, so m[un]lock
+can skip these pages by testing the page mapping under page lock.
+
+To complete page migration, we place the new and old pages back onto the LRU
+after dropping the page lock.  The "unneeded" page - old page on success, new
+page on failure - will be freed when the reference count held by the migration
+process is released.  To ensure that we don't strand pages on the unevictable
+list because of a race between munlock and migration, page migration uses the
+putback_lru_page() function to add migrated pages back to the LRU.
+
+
+mmap(MAP_LOCKED) SYSTEM CALL HANDLING
+-------------------------------------
 
 In addition the the mlock()/mlockall() system calls, an application can request
-that a region of memory be mlocked using the MAP_LOCKED flag with the mmap()
+that a region of memory be mlocked supplying the MAP_LOCKED flag to the mmap()
 call.  Furthermore, any mmap() call or brk() call that expands the heap by a
 task that has previously called mlockall() with the MCL_FUTURE flag will result
-in the newly mapped memory being mlocked.  Before the unevictable/mlock changes,
-the kernel simply called make_pages_present() to allocate pages and populate
-the page table.
+in the newly mapped memory being mlocked.  Before the unevictable/mlock
+changes, the kernel simply called make_pages_present() to allocate pages and
+populate the page table.
 
 To mlock a range of memory under the unevictable/mlock infrastructure, the
 mmap() handler and task address space expansion functions call
 mlock_vma_pages_range() specifying the vma and the address range to mlock.
-mlock_vma_pages_range() filters vmas like mlock_fixup(), as described above in
-"Mlocked Pages:  Filtering Vmas".  It will clear the VM_LOCKED flag, which will
-have already been set by the caller, in filtered vmas.  Thus these vma's need
-not be visited for munlock when the region is unmapped.
+mlock_vma_pages_range() filters VMAs like mlock_fixup(), as described above in
+"Filtering Special VMAs".  It will clear the VM_LOCKED flag, which will have
+already been set by the caller, in filtered VMAs.  Thus these VMA's need not be
+visited for munlock when the region is unmapped.
 
-For "normal" vmas, mlock_vma_pages_range() calls __mlock_vma_pages_range() to
+For "normal" VMAs, mlock_vma_pages_range() calls __mlock_vma_pages_range() to
 fault/allocate the pages and mlock them.  Again, like mlock_fixup(),
 mlock_vma_pages_range() downgrades the mmap semaphore to read mode before
-attempting to fault/allocate and mlock the pages; and "upgrades" the semaphore
+attempting to fault/allocate and mlock the pages and "upgrades" the semaphore
 back to write mode before returning.
 
-The callers of mlock_vma_pages_range() will have already added the memory
-range to be mlocked to the task's "locked_vm".  To account for filtered vmas,
+The callers of mlock_vma_pages_range() will have already added the memory range
+to be mlocked to the task's "locked_vm".  To account for filtered VMAs,
 mlock_vma_pages_range() returns the number of pages NOT mlocked.  All of the
-callers then subtract a non-negative return value from the task's locked_vm.
-A negative return value represent an error--for example, from get_user_pages()
-attempting to fault in a vma with PROT_NONE access.  In this case, we leave
-the memory range accounted as locked_vm, as the protections could be changed
-later and pages allocated into that region.
+callers then subtract a non-negative return value from the task's locked_vm.  A
+negative return value represent an error - for example, from get_user_pages()
+attempting to fault in a VMA with PROT_NONE access.  In this case, we leave the
+memory range accounted as locked_vm, as the protections could be changed later
+and pages allocated into that region.
 
 
-Mlocked Pages:  munmap()/exit()/exec() System Call Handling
+munmap()/exit()/exec() SYSTEM CALL HANDLING
+-------------------------------------------
 
 When unmapping an mlocked region of memory, whether by an explicit call to
 munmap() or via an internal unmap from exit() or exec() processing, we must
-munlock the pages if we're removing the last VM_LOCKED vma that maps the pages.
+munlock the pages if we're removing the last VM_LOCKED VMA that maps the pages.
 Before the unevictable/mlock changes, mlocking did not mark the pages in any
 way, so unmapping them required no processing.
 
 To munlock a range of memory under the unevictable/mlock infrastructure, the
-munmap() hander and task address space tear down function call
+munmap() handler and task address space call tear down function
 munlock_vma_pages_all().  The name reflects the observation that one always
-specifies the entire vma range when munlock()ing during unmap of a region.
-Because of the vma filtering when mlocking() regions, only "normal" vmas that
+specifies the entire VMA range when munlock()ing during unmap of a region.
+Because of the VMA filtering when mlocking() regions, only "normal" VMAs that
 actually contain mlocked pages will be passed to munlock_vma_pages_all().
 
-munlock_vma_pages_all() clears the VM_LOCKED vma flag and, like mlock_fixup()
+munlock_vma_pages_all() clears the VM_LOCKED VMA flag and, like mlock_fixup()
 for the munlock case, calls __munlock_vma_pages_range() to walk the page table
-for the vma's memory range and munlock_vma_page() each resident page mapped by
-the vma.  This effectively munlocks the page, only if this is the last
-VM_LOCKED vma that maps the page.
-
+for the VMA's memory range and munlock_vma_page() each resident page mapped by
+the VMA.  This effectively munlocks the page, only if this is the last
+VM_LOCKED VMA that maps the page.
 
-Mlocked Page:  try_to_unmap()
 
-[Note:  the code changes represented by this section are really quite small
-compared to the text to describe what happening and why, and to discuss the
-implications.]
+try_to_unmap()
+--------------
 
-Pages can, of course, be mapped into multiple vmas.  Some of these vmas may
+Pages can, of course, be mapped into multiple VMAs.  Some of these VMAs may
 have VM_LOCKED flag set.  It is possible for a page mapped into one or more
-VM_LOCKED vmas not to have the PG_mlocked flag set and therefore reside on one
-of the active or inactive LRU lists.  This could happen if, for example, a
-task in the process of munlock()ing the page could not isolate the page from
-the LRU.  As a result, vmscan/shrink_page_list() might encounter such a page
-as described in "Unevictable Pages and Vmscan [shrink_*_list()]".  To
-handle this situation, try_to_unmap() has been enhanced to check for VM_LOCKED
-vmas while it is walking a page's reverse map.
+VM_LOCKED VMAs not to have the PG_mlocked flag set and therefore reside on one
+of the active or inactive LRU lists.  This could happen if, for example, a task
+in the process of munlocking the page could not isolate the page from the LRU.
+As a result, vmscan/shrink_page_list() might encounter such a page as described
+in section "vmscan's handling of unevictable pages".  To handle this situation,
+try_to_unmap() checks for VM_LOCKED VMAs while it is walking a page's reverse
+map.
 
 try_to_unmap() is always called, by either vmscan for reclaim or for page
-migration, with the argument page locked and isolated from the LRU.  BUG_ON()
-assertions enforce this requirement.  Separate functions handle anonymous and
-mapped file pages, as these types of pages have different reverse map
-mechanisms.
-
-	try_to_unmap_anon()
-
-To unmap anonymous pages, each vma in the list anchored in the anon_vma must be
-visited--at least until a VM_LOCKED vma is encountered.  If the page is being
-unmapped for migration, VM_LOCKED vmas do not stop the process because mlocked
-pages are migratable.  However, for reclaim, if the page is mapped into a
-VM_LOCKED vma, the scan stops.  try_to_unmap() attempts to acquire the mmap
-semphore of the mm_struct to which the vma belongs in read mode.  If this is
-successful, try_to_unmap() will mlock the page via mlock_vma_page()--we
-wouldn't have gotten to try_to_unmap() if the page were already mlocked--and
-will return SWAP_MLOCK, indicating that the page is unevictable.  If the
-mmap semaphore cannot be acquired, we are not sure whether the page is really
-unevictable or not.  In this case, try_to_unmap() will return SWAP_AGAIN.
-
-	try_to_unmap_file() -- linear mappings
-
-Unmapping of a mapped file page works the same, except that the scan visits
-all vmas that maps the page's index/page offset in the page's mapping's
-reverse map priority search tree.  It must also visit each vma in the page's
-mapping's non-linear list, if the list is non-empty.  As for anonymous pages,
-on encountering a VM_LOCKED vma for a mapped file page, try_to_unmap() will
-attempt to acquire the associated mm_struct's mmap semaphore to mlock the page,
-returning SWAP_MLOCK if this is successful, and SWAP_AGAIN, if not.
-
-	try_to_unmap_file() -- non-linear mappings
-
-If a page's mapping contains a non-empty non-linear mapping vma list, then
-try_to_un{map|lock}() must also visit each vma in that list to determine
-whether the page is mapped in a VM_LOCKED vma.  Again, the scan must visit
-all vmas in the non-linear list to ensure that the pages is not/should not be
-mlocked.  If a VM_LOCKED vma is found in the list, the scan could terminate.
-However, there is no easy way to determine whether the page is actually mapped
-in a given vma--either for unmapping or testing whether the VM_LOCKED vma
-actually pins the page.
-
-So, try_to_unmap_file() handles non-linear mappings by scanning a certain
-number of pages--a "cluster"--in each non-linear vma associated with the page's
-mapping, for each file mapped page that vmscan tries to unmap.  If this happens
-to unmap the page we're trying to unmap, try_to_unmap() will notice this on
-return--(page_mapcount(page) == 0)--and return SWAP_SUCCESS.  Otherwise, it
-will return SWAP_AGAIN, causing vmscan to recirculate this page.  We take
-advantage of the cluster scan in try_to_unmap_cluster() as follows:
-
-For each non-linear vma, try_to_unmap_cluster() attempts to acquire the mmap
-semaphore of the associated mm_struct for read without blocking.  If this
-attempt is successful and the vma is VM_LOCKED, try_to_unmap_cluster() will
-retain the mmap semaphore for the scan; otherwise it drops it here.  Then,
-for each page in the cluster, if we're holding the mmap semaphore for a locked
-vma, try_to_unmap_cluster() calls mlock_vma_page() to mlock the page.  This
-call is a no-op if the page is already locked, but will mlock any pages in
-the non-linear mapping that happen to be unlocked.  If one of the pages so
-mlocked is the page passed in to try_to_unmap(), try_to_unmap_cluster() will
-return SWAP_MLOCK, rather than the default SWAP_AGAIN.  This will allow vmscan
-to cull the page, rather than recirculating it on the inactive list.  Again,
-if try_to_unmap_cluster() cannot acquire the vma's mmap sem, it returns
-SWAP_AGAIN, indicating that the page is mapped by a VM_LOCKED vma, but
-couldn't be mlocked.
-
-
-Mlocked pages:  try_to_munlock() Reverse Map Scan
-
-TODO/FIXME:  a better name might be page_mlocked()--analogous to the
-page_referenced() reverse map walker.
-
-When munlock_vma_page()--see "Mlocked Pages:  munlock()/munlockall()
-System Call Handling" above--tries to munlock a page, it needs to
-determine whether or not the page is mapped by any VM_LOCKED vma, without
-actually attempting to unmap all ptes from the page.  For this purpose, the
-unevictable/mlock infrastructure introduced a variant of try_to_unmap() called
-try_to_munlock().
+migration, with the argument page locked and isolated from the LRU.  Separate
+functions handle anonymous and mapped file pages, as these types of pages have
+different reverse map mechanisms.
+
+ (*) try_to_unmap_anon()
+
+     To unmap anonymous pages, each VMA in the list anchored in the anon_vma
+     must be visited - at least until a VM_LOCKED VMA is encountered.  If the
+     page is being unmapped for migration, VM_LOCKED VMAs do not stop the
+     process because mlocked pages are migratable.  However, for reclaim, if
+     the page is mapped into a VM_LOCKED VMA, the scan stops.
+
+     try_to_unmap_anon() attempts to acquire in read mode the mmap semphore of
+     the mm_struct to which the VMA belongs.  If this is successful, it will
+     mlock the page via mlock_vma_page() - we wouldn't have gotten to
+     try_to_unmap_anon() if the page were already mlocked - and will return
+     SWAP_MLOCK, indicating that the page is unevictable.
+
+     If the mmap semaphore cannot be acquired, we are not sure whether the page
+     is really unevictable or not.  In this case, try_to_unmap_anon() will
+     return SWAP_AGAIN.
+
+ (*) try_to_unmap_file() - linear mappings
+
+     Unmapping of a mapped file page works the same as for anonymous mappings,
+     except that the scan visits all VMAs that map the page's index/page offset
+     in the page's mapping's reverse map priority search tree.  It also visits
+     each VMA in the page's mapping's non-linear list, if the list is
+     non-empty.
+
+     As for anonymous pages, on encountering a VM_LOCKED VMA for a mapped file
+     page, try_to_unmap_file() will attempt to acquire the associated
+     mm_struct's mmap semaphore to mlock the page, returning SWAP_MLOCK if this
+     is successful, and SWAP_AGAIN, if not.
+
+ (*) try_to_unmap_file() - non-linear mappings
+
+     If a page's mapping contains a non-empty non-linear mapping VMA list, then
+     try_to_un{map|lock}() must also visit each VMA in that list to determine
+     whether the page is mapped in a VM_LOCKED VMA.  Again, the scan must visit
+     all VMAs in the non-linear list to ensure that the pages is not/should not
+     be mlocked.
+
+     If a VM_LOCKED VMA is found in the list, the scan could terminate.
+     However, there is no easy way to determine whether the page is actually
+     mapped in a given VMA - either for unmapping or testing whether the
+     VM_LOCKED VMA actually pins the page.
+
+     try_to_unmap_file() handles non-linear mappings by scanning a certain
+     number of pages - a "cluster" - in each non-linear VMA associated with the
+     page's mapping, for each file mapped page that vmscan tries to unmap.  If
+     this happens to unmap the page we're trying to unmap, try_to_unmap() will
+     notice this on return (page_mapcount(page) will be 0) and return
+     SWAP_SUCCESS.  Otherwise, it will return SWAP_AGAIN, causing vmscan to
+     recirculate this page.  We take advantage of the cluster scan in
+     try_to_unmap_cluster() as follows:
+
+	For each non-linear VMA, try_to_unmap_cluster() attempts to acquire the
+	mmap semaphore of the associated mm_struct for read without blocking.
+
+	If this attempt is successful and the VMA is VM_LOCKED,
+	try_to_unmap_cluster() will retain the mmap semaphore for the scan;
+	otherwise it drops it here.
+
+	Then, for each page in the cluster, if we're holding the mmap semaphore
+	for a locked VMA, try_to_unmap_cluster() calls mlock_vma_page() to
+	mlock the page.  This call is a no-op if the page is already locked,
+	but will mlock any pages in the non-linear mapping that happen to be
+	unlocked.
+
+	If one of the pages so mlocked is the page passed in to try_to_unmap(),
+	try_to_unmap_cluster() will return SWAP_MLOCK, rather than the default
+	SWAP_AGAIN.  This will allow vmscan to cull the page, rather than
+	recirculating it on the inactive list.
+
+	Again, if try_to_unmap_cluster() cannot acquire the VMA's mmap sem, it
+	returns SWAP_AGAIN, indicating that the page is mapped by a VM_LOCKED
+	VMA, but couldn't be mlocked.
+
+
+try_to_munlock() REVERSE MAP SCAN
+---------------------------------
+
+ [!] TODO/FIXME: a better name might be page_mlocked() - analogous to the
+     page_referenced() reverse map walker.
+
+When munlock_vma_page() [see section "munlock()/munlockall() System Call
+Handling" above] tries to munlock a page, it needs to determine whether or not
+the page is mapped by any VM_LOCKED VMA without actually attempting to unmap
+all PTEs from the page.  For this purpose, the unevictable/mlock infrastructure
+introduced a variant of try_to_unmap() called try_to_munlock().
 
 try_to_munlock() calls the same functions as try_to_unmap() for anonymous and
 mapped file pages with an additional argument specifing unlock versus unmap
 processing.  Again, these functions walk the respective reverse maps looking
-for VM_LOCKED vmas.  When such a vma is found for anonymous pages and file
+for VM_LOCKED VMAs.  When such a VMA is found for anonymous pages and file
 pages mapped in linear VMAs, as in the try_to_unmap() case, the functions
 attempt to acquire the associated mmap semphore, mlock the page via
 mlock_vma_page() and return SWAP_MLOCK.  This effectively undoes the
 pre-clearing of the page's PG_mlocked done by munlock_vma_page.
 
-If try_to_unmap() is unable to acquire a VM_LOCKED vma's associated mmap
-semaphore, it will return SWAP_AGAIN.  This will allow shrink_page_list()
-to recycle the page on the inactive list and hope that it has better luck
-with the page next time.
-
-For file pages mapped into non-linear vmas, the try_to_munlock() logic works
-slightly differently.  On encountering a VM_LOCKED non-linear vma that might
-map the page, try_to_munlock() returns SWAP_AGAIN without actually mlocking
-the page.  munlock_vma_page() will just leave the page unlocked and let
-vmscan deal with it--the usual fallback position.
-
-Note that try_to_munlock()'s reverse map walk must visit every vma in a pages'
-reverse map to determine that a page is NOT mapped into any VM_LOCKED vma.
-However, the scan can terminate when it encounters a VM_LOCKED vma and can
-successfully acquire the vma's mmap semphore for read and mlock the page.
-Although try_to_munlock() can be called many [very many!] times when
-munlock()ing a large region or tearing down a large address space that has been
-mlocked via mlockall(), overall this is a fairly rare event.
-
-Mlocked Page:  Page Reclaim in shrink_*_list()
-
-shrink_active_list() culls any obviously unevictable pages--i.e.,
-!page_evictable(page, NULL)--diverting these to the unevictable lru
-list.  However, shrink_active_list() only sees unevictable pages that
-made it onto the active/inactive lru lists.  Note that these pages do not
-have PageUnevictable set--otherwise, they would be on the unevictable list and
-shrink_active_list would never see them.
+If try_to_unmap() is unable to acquire a VM_LOCKED VMA's associated mmap
+semaphore, it will return SWAP_AGAIN.  This will allow shrink_page_list() to
+recycle the page on the inactive list and hope that it has better luck with the
+page next time.
+
+For file pages mapped into non-linear VMAs, the try_to_munlock() logic works
+slightly differently.  On encountering a VM_LOCKED non-linear VMA that might
+map the page, try_to_munlock() returns SWAP_AGAIN without actually mlocking the
+page.  munlock_vma_page() will just leave the page unlocked and let vmscan deal
+with it - the usual fallback position.
+
+Note that try_to_munlock()'s reverse map walk must visit every VMA in a page's
+reverse map to determine that a page is NOT mapped into any VM_LOCKED VMA.
+However, the scan can terminate when it encounters a VM_LOCKED VMA and can
+successfully acquire the VMA's mmap semphore for read and mlock the page.
+Although try_to_munlock() might be called a great many times when munlocking a
+large region or tearing down a large address space that has been mlocked via
+mlockall(), overall this is a fairly rare event.
+
+
+PAGE RECLAIM IN shrink_*_list()
+-------------------------------
+
+shrink_active_list() culls any obviously unevictable pages - i.e.
+!page_evictable(page, NULL) - diverting these to the unevictable list.
+However, shrink_active_list() only sees unevictable pages that made it onto the
+active/inactive lru lists.  Note that these pages do not have PageUnevictable
+set - otherwise they would be on the unevictable list and shrink_active_list
+would never see them.
 
 Some examples of these unevictable pages on the LRU lists are:
 
-1) ramfs pages that have been placed on the lru lists when first allocated.
+ (1) ramfs pages that have been placed on the LRU lists when first allocated.
+
+ (2) SHM_LOCK'd shared memory pages.  shmctl(SHM_LOCK) does not attempt to
+     allocate or fault in the pages in the shared memory region.  This happens
+     when an application accesses the page the first time after SHM_LOCK'ing
+     the segment.
 
-2) SHM_LOCKed shared memory pages.  shmctl(SHM_LOCK) does not attempt to
-   allocate or fault in the pages in the shared memory region.  This happens
-   when an application accesses the page the first time after SHM_LOCKing
-   the segment.
+ (3) mlocked pages that could not be isolated from the LRU and moved to the
+     unevictable list in mlock_vma_page().
 
-3) Mlocked pages that could not be isolated from the lru and moved to the
-   unevictable list in mlock_vma_page().
+ (4) Pages mapped into multiple VM_LOCKED VMAs, but try_to_munlock() couldn't
+     acquire the VMA's mmap semaphore to test the flags and set PageMlocked.
+     munlock_vma_page() was forced to let the page back on to the normal LRU
+     list for vmscan to handle.
 
-3) Pages mapped into multiple VM_LOCKED vmas, but try_to_munlock() couldn't
-   acquire the vma's mmap semaphore to test the flags and set PageMlocked.
-   munlock_vma_page() was forced to let the page back on to the normal
-   LRU list for vmscan to handle.
+shrink_inactive_list() also diverts any unevictable pages that it finds on the
+inactive lists to the appropriate zone's unevictable list.
 
-shrink_inactive_list() also culls any unevictable pages that it finds on
-the inactive lists, again diverting them to the appropriate zone's unevictable
-lru list.  shrink_inactive_list() should only see SHM_LOCKed pages that became
-SHM_LOCKed after shrink_active_list() had moved them to the inactive list, or
-pages mapped into VM_LOCKED vmas that munlock_vma_page() couldn't isolate from
-the lru to recheck via try_to_munlock().  shrink_inactive_list() won't notice
-the latter, but will pass on to shrink_page_list().
+shrink_inactive_list() should only see SHM_LOCK'd pages that became SHM_LOCK'd
+after shrink_active_list() had moved them to the inactive list, or pages mapped
+into VM_LOCKED VMAs that munlock_vma_page() couldn't isolate from the LRU to
+recheck via try_to_munlock().  shrink_inactive_list() won't notice the latter,
+but will pass on to shrink_page_list().
 
 shrink_page_list() again culls obviously unevictable pages that it could
 encounter for similar reason to shrink_inactive_list().  Pages mapped into
-VM_LOCKED vmas but without PG_mlocked set will make it all the way to
+VM_LOCKED VMAs but without PG_mlocked set will make it all the way to
 try_to_unmap().  shrink_page_list() will divert them to the unevictable list
 when try_to_unmap() returns SWAP_MLOCK, as discussed above.