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* zram: cosmetic: cleanup documentationSergey Senozhatsky2016-07-261-46/+45
| | | | | | | | | | | | | zram documentation is a mix of different styles: spaces, tabs, tabs + spaces, etc. Clean it up. Link: http://lkml.kernel.org/r/20160531122017.2878-6-sergey.senozhatsky@gmail.com Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Jonathan Corbet <corbet@lwn.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zram: use crypto api to check alg availabilitySergey Senozhatsky2016-07-261-0/+11
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | There is no way to get a string with all the crypto comp algorithms supported by the crypto comp engine, so we need to maintain our own backends list. At the same time we additionally need to use crypto_has_comp() to make sure that the user has requested a compression algorithm that is recognized by the crypto comp engine. Relying on /proc/crypto is not an options here, because it does not show not-yet-inserted compression modules. Example: modprobe zram cat /proc/crypto | grep -i lz4 modprobe lz4 cat /proc/crypto | grep -i lz4 name : lz4 driver : lz4-generic module : lz4 So the user can't tell exactly if the lz4 is really supported from /proc/crypto output, unless someone or something has loaded it. This patch also adds crypto_has_comp() to zcomp_available_show(). We store all the compression algorithms names in zcomp's `backends' array, regardless the CONFIG_CRYPTO_FOO configuration, but show only those that are also supported by crypto engine. This helps user to know the exact list of compression algorithms that can be used. Example: module lz4 is not loaded yet, but is supported by the crypto engine. /proc/crypto has no information on this module, while zram's `comp_algorithm' lists it: cat /proc/crypto | grep -i lz4 cat /sys/block/zram0/comp_algorithm [lzo] lz4 deflate lz4hc 842 We still use the `backends' array to determine if the requested compression backend is known to crypto api. This array, however, may not contain some entries, therefore as the last step we call crypto_has_comp() function which attempts to insmod the requested compression algorithm to determine if crypto api supports it. The advantage of this method is that now we permit the usage of out-of-tree crypto compression modules (implementing S/W or H/W compression). [sergey.senozhatsky@gmail.com: zram-use-crypto-api-to-check-alg-availability-v3] Link: http://lkml.kernel.org/r/20160604024902.11778-4-sergey.senozhatsky@gmail.com Link: http://lkml.kernel.org/r/20160531122017.2878-5-sergey.senozhatsky@gmail.com Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zram: introduce per-device debug_stat sysfs nodeSergey Senozhatsky2016-05-201-0/+1
| | | | | | | | | | | | | | | | | | | | | debug_stat sysfs is read-only and represents various debugging data that zram developers may need. This file is not meant to be used by anyone else: its content is not documented and will change any time w/o any notice. Therefore, the output of debug_stat file contains a version string. To avoid any confusion, we will increase the version number every time we modify the output. At the moment this file exports only one value -- the number of re-compressions, IOW, the number of times compression fast path has failed. This stat is temporary any will be useful in case if any per-cpu compression streams regressions will be reported. Link: http://lkml.kernel.org/r/20160513230834.GB26763@bbox Link: http://lkml.kernel.org/r/20160511134553.12655-1-sergey.senozhatsky@gmail.com Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zram: remove max_comp_streams internalsSergey Senozhatsky2016-05-201-19/+8
| | | | | | | | | | | | | | | | | | | | | | | | | | | Remove the internal part of max_comp_streams interface, since we switched to per-cpu streams. We will keep RW max_comp_streams attr around, because: a) we may (silently) switch back to idle compression streams list and don't want to disturb user space b) max_comp_streams attr must wait for the next 'lay off cycle'; we give user space 2 years to adjust before we remove/downgrade the attr, and there are already several attrs scheduled for removal in 4.11, so it's too late for max_comp_streams. This slightly change a user visible behaviour: - First, reading from max_comp_stream file now will always return the number of online CPUs. - Second, writing to max_comp_stream will not take any effect. Link: http://lkml.kernel.org/r/20160503165546.25201-1-sergey.senozhatsky@gmail.com Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zram: update documentationSergey SENOZHATSKY2015-09-241-4/+40
| | | | | | | | | | | | | | | | Several documentation changes. First, we never mentioned any errors and never required any error checks in documentation. Second, mention that there is another way to configure and manage zram devices -- zramctl, provided by util-linux. Third, add a bit of clarification on why `mem_used_max' attr is RW and correct some typos. Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
* zsmalloc: account the number of compacted pagesSergey Senozhatsky2015-09-081-1/+2
| | | | | | | | | | | | | | | | | | | | | Compaction returns back to zram the number of migrated objects, which is quite uninformative -- we have objects of different sizes so user space cannot obtain any valuable data from that number. Change compaction to operate in terms of pages and return back to compaction issuer the number of pages that were freed during compaction. So from now on we will export more meaningful value in zram<id>/mm_stat -- the number of freed (compacted) pages. This requires: (a) a rename of `num_migrated' to 'pages_compacted' (b) a internal API change -- return first_page's fullness_group from putback_zspage(), so we know when putback_zspage() did free_zspage(). It helps us to account compaction stats correctly. Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zram: add dynamic device add/remove functionalitySergey Senozhatsky2015-06-251-3/+20
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | We currently don't support on-demand device creation. The one and only way to have N zram devices is to specify num_devices module parameter (default value: 1). IOW if, for some reason, at some point, user wants to have N + 1 devies he/she must umount all the existing devices, unload the module, load the module passing num_devices equals to N + 1. And do this again, if needed. This patch introduces zram control sysfs class, which has two sysfs attrs: - hot_add -- add a new zram device - hot_remove -- remove a specific (device_id) zram device hot_add sysfs attr is read-only and has only automatic device id assignment mode (as requested by Minchan Kim). read operation performed on this attr creates a new zram device and returns back its device_id or error status. Usage example: # add a new specific zram device cat /sys/class/zram-control/hot_add 2 # remove a specific zram device echo 4 > /sys/class/zram-control/hot_remove Returning zram_add() error code back to user (-ENOMEM in this case) cat /sys/class/zram-control/hot_add cat: /sys/class/zram-control/hot_add: Cannot allocate memory NOTE, there might be users who already depend on the fact that at least zram0 device gets always created by zram_init(). Preserve this behavior. [minchan@kernel.org: use zram->claim to avoid lockdep splat] Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zram: remove max_num_devices limitationSergey Senozhatsky2015-06-251-1/+3
| | | | | | | | | | | Limiting the number of zram devices to 32 (default max_num_devices value) is confusing, let's drop it. A user with 2TB or 4TB of RAM, for example, can request as many devices as he can handle. Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zram: add `compact` sysfs entry to documentationSergey Senozhatsky2015-06-251-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | We currently don't support zram on-demand device creation. The only way to have N zram devices is to specify num_devices module parameter (default value 1). That means that if, for some reason, at some point, user wants to have N + 1 devies he/she must umount all the existing devices, unload the module, load the module passing num_devices equals to N + 1. This patchset introduces zram-control sysfs class, which has two sysfs attrs: - hot_add -- add a new zram device - hot_remove -- remove a specific (device_id) zram device Usage example: # add a new specific zram device cat /sys/class/zram-control/hot_add 1 # remove a specific zram device echo 4 > /sys/class/zram-control/hot_remove This patch (of 10): Briefly describe missing `compact` sysfs entry. Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zram: deprecate zram attrs sysfs nodesSergey Senozhatsky2015-04-151-0/+16
| | | | | | | | | | | | | | | | | | | | | | Add Documentation/ABI/obsolete/sysfs-block-zram file and list obsolete and deprecated attributes there. The patch also adds additional information to zram documentation and describes the basic strategy: - the existing RW nodes will be downgraded to WO nodes (in 4.11) - deprecated RO sysfs nodes will eventually be removed (in 4.11) Users will be additionally notified about deprecated attr usage by pr_warn_once() (added to every deprecated attr _show()), as suggested by Minchan Kim. User space is advised to use zram<id>/stat, zram<id>/io_stat and zram<id>/mm_stat files. Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Reported-by: Minchan Kim <minchan@kernel.org> Cc: Nitin Gupta <ngupta@vflare.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zram: export new 'mm_stat' sysfs attrsSergey Senozhatsky2015-04-151-0/+12
| | | | | | | | | | | | | | | | | | | | | Per-device `zram<id>/mm_stat' file provides mm statistics of a particular zram device in a format similar to block layer statistics. The file consists of a single line and represents the following stats (separated by whitespace): orig_data_size compr_data_size mem_used_total mem_limit mem_used_max zero_pages num_migrated Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Cc: Nitin Gupta <ngupta@vflare.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zram: export new 'io_stat' sysfs attrsSergey Senozhatsky2015-04-151-0/+11
| | | | | | | | | | | | | | | | | | Per-device `zram<id>/io_stat' file provides accumulated I/O statistics of particular zram device in a format similar to block layer statistics. The file consists of a single line and represents the following stats (separated by whitespace): failed_reads failed_writes invalid_io notify_free Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Cc: Nitin Gupta <ngupta@vflare.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zram: describe device attrs in documentationSergey Senozhatsky2015-04-151-14/+34
| | | | | | | | | | | | | | | | | | | | Briefly describe exported device stat attrs in zram documentation. We will eventually get rid of per-stat sysfs nodes and, thus, clean up Documentation/ABI/testing/sysfs-block-zram file, which is the only source of information about device sysfs nodes. Add `num_migrated' description, since there is no independent `num_migrated' sysfs node (and no corresponding sysfs-block-zram entry), it will be exported via zram<id>/mm_stat file. At this point we can provide minimal description, because sysfs-block-zram still contains detailed information. Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Cc: Nitin Gupta <ngupta@vflare.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zram: report maximum used memoryMinchan Kim2014-10-091-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | Normally, zram user could get maximum memory usage zram consumed via polling mem_used_total with sysfs in userspace. But it has a critical problem because user can miss peak memory usage during update inverval of polling. For avoiding that, user should poll it with shorter interval(ie, 0.0000000001s) with mlocking to avoid page fault delay when memory pressure is heavy. It would be troublesome. This patch adds new knob "mem_used_max" so user could see the maximum memory usage easily via reading the knob and reset it via "echo 0 > /sys/block/zram0/mem_used_max". Signed-off-by: Minchan Kim <minchan@kernel.org> Reviewed-by: Dan Streetman <ddstreet@ieee.org> Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Jerome Marchand <jmarchan@redhat.com> Cc: <juno.choi@lge.com> Cc: <seungho1.park@lge.com> Cc: Luigi Semenzato <semenzato@google.com> Cc: Nitin Gupta <ngupta@vflare.org> Cc: Seth Jennings <sjennings@variantweb.net> Reviewed-by: David Horner <ds2horner@gmail.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zram: zram memory size limitationMinchan Kim2014-10-091-4/+20
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | Since zram has no control feature to limit memory usage, it makes hard to manage system memrory. This patch adds new knob "mem_limit" via sysfs to set up the a limit so that zram could fail allocation once it reaches the limit. In addition, user could change the limit in runtime so that he could manage the memory more dynamically. Initial state is no limit so it doesn't break old behavior. [akpm@linux-foundation.org: fix typo, per Sergey] Signed-off-by: Minchan Kim <minchan@kernel.org> Cc: Dan Streetman <ddstreet@ieee.org> Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Jerome Marchand <jmarchan@redhat.com> Cc: <juno.choi@lge.com> Cc: <seungho1.park@lge.com> Cc: Luigi Semenzato <semenzato@google.com> Cc: Nitin Gupta <ngupta@vflare.org> Cc: Seth Jennings <sjennings@variantweb.net> Cc: David Horner <ds2horner@gmail.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zram: propagate error to userMinchan Kim2014-04-071-4/+5
| | | | | | | | | | | | | | | | | | | | | When we initialized zcomp with single, we couldn't change max_comp_streams without zram reset but current interface doesn't show any error to user and even it changes max_comp_streams's value without any effect so it would make user very confusing. This patch prevents max_comp_streams's change when zcomp was initialized as single zcomp and emit the error to user(ex, echo). [akpm@linux-foundation.org: don't return with the lock held, per Sergey] [fengguang.wu@intel.com: fix coccinelle warnings] Signed-off-by: Minchan Kim <minchan@kernel.org> Cc: Nitin Gupta <ngupta@vflare.org> Cc: Jerome Marchand <jmarchan@redhat.com> Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Fengguang Wu <fengguang.wu@intel.com> Cc: Stephen Rothwell <sfr@canb.auug.org.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zram: make compression algorithm selection possibleSergey Senozhatsky2014-04-071-5/+19
| | | | | | | | | | | | | | | | | | | Add and document `comp_algorithm' device attribute. This attribute allows to show supported compression and currently selected compression algorithms: cat /sys/block/zram0/comp_algorithm [lzo] lz4 and change selected compression algorithm: echo lzo > /sys/block/zram0/comp_algorithm Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Cc: Jerome Marchand <jmarchan@redhat.com> Cc: Nitin Gupta <ngupta@vflare.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zram: add multi stream functionalitySergey Senozhatsky2014-04-071-5/+26
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Existing zram (zcomp) implementation has only one compression stream (buffer and algorithm private part), so in order to prevent data corruption only one write (compress operation) can use this compression stream, forcing all concurrent write operations to wait for stream lock to be released. This patch changes zcomp to keep a compression streams list of user-defined size (via sysfs device attr). Each write operation still exclusively holds compression stream, the difference is that we can have N write operations (depending on size of streams list) executing in parallel. See TEST section later in commit message for performance data. Introduce struct zcomp_strm_multi and a set of functions to manage zcomp_strm stream access. zcomp_strm_multi has a list of idle zcomp_strm structs, spinlock to protect idle list and wait queue, making it possible to perform parallel compressions. The following set of functions added: - zcomp_strm_multi_find()/zcomp_strm_multi_release() find and release a compression stream, implement required locking - zcomp_strm_multi_create()/zcomp_strm_multi_destroy() create and destroy zcomp_strm_multi zcomp ->strm_find() and ->strm_release() callbacks are set during initialisation to zcomp_strm_multi_find()/zcomp_strm_multi_release() correspondingly. Each time zcomp issues a zcomp_strm_multi_find() call, the following set of operations performed: - spin lock strm_lock - if idle list is not empty, remove zcomp_strm from idle list, spin unlock and return zcomp stream pointer to caller - if idle list is empty, current adds itself to wait queue. it will be awaken by zcomp_strm_multi_release() caller. zcomp_strm_multi_release(): - spin lock strm_lock - add zcomp stream to idle list - spin unlock, wake up sleeper Minchan Kim reported that spinlock-based locking scheme has demonstrated a severe perfomance regression for single compression stream case, comparing to mutex-based (see https://lkml.org/lkml/2014/2/18/16) base spinlock mutex ==Initial write ==Initial write ==Initial write records: 5 records: 5 records: 5 avg: 1642424.35 avg: 699610.40 avg: 1655583.71 std: 39890.95(2.43%) std: 232014.19(33.16%) std: 52293.96 max: 1690170.94 max: 1163473.45 max: 1697164.75 min: 1568669.52 min: 573429.88 min: 1553410.23 ==Rewrite ==Rewrite ==Rewrite records: 5 records: 5 records: 5 avg: 1611775.39 avg: 501406.64 avg: 1684419.11 std: 17144.58(1.06%) std: 15354.41(3.06%) std: 18367.42 max: 1641800.95 max: 531356.78 max: 1706445.84 min: 1593515.27 min: 488817.78 min: 1655335.73 When only one compression stream available, mutex with spin on owner tends to perform much better than frequent wait_event()/wake_up(). This is why single stream implemented as a special case with mutex locking. Introduce and document zram device attribute max_comp_streams. This attr shows and stores current zcomp's max number of zcomp streams (max_strm). Extend zcomp's zcomp_create() with `max_strm' parameter. `max_strm' limits the number of zcomp_strm structs in compression backend's idle list (max_comp_streams). max_comp_streams used during initialisation as follows: -- passing to zcomp_create() max_strm equals to 1 will initialise zcomp using single compression stream zcomp_strm_single (mutex-based locking). -- passing to zcomp_create() max_strm greater than 1 will initialise zcomp using multi compression stream zcomp_strm_multi (spinlock-based locking). default max_comp_streams value is 1, meaning that zram with single stream will be initialised. Later patch will introduce configuration knob to change max_comp_streams on already initialised and used zcomp. TEST iozone -t 3 -R -r 16K -s 60M -I +Z test base 1 strm (mutex) 3 strm (spinlock) ----------------------------------------------------------------------- Initial write 589286.78 583518.39 718011.05 Rewrite 604837.97 596776.38 1515125.72 Random write 584120.11 595714.58 1388850.25 Pwrite 535731.17 541117.38 739295.27 Fwrite 1418083.88 1478612.72 1484927.06 Usage example: set max_comp_streams to 4 echo 4 > /sys/block/zram0/max_comp_streams show current max_comp_streams (default value is 1). cat /sys/block/zram0/max_comp_streams Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Cc: Jerome Marchand <jmarchan@redhat.com> Cc: Nitin Gupta <ngupta@vflare.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zram: document failed_reads, failed_writes statsSergey Senozhatsky2014-04-071-1/+2
| | | | | | | | | | | | Document `failed_reads' and `failed_writes' device attributes. Remove info about `discard' - there is no such zram attr. Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Jerome Marchand <jmarchan@redhat.com> Cc: Nitin Gupta <ngupta@vflare.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zram: move zram size warning to documentationSergey Senozhatsky2014-04-071-0/+5
| | | | | | | | | | | | Move zram warning about disksize and size of memory correlation to zram documentation. Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Cc: Jerome Marchand <jmarchan@redhat.com> Cc: Nitin Gupta <ngupta@vflare.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zram: remove old private project commentMinchan Kim2014-01-301-6/+0
| | | | | | | | | | Remove the old private compcache project address so upcoming patches should be sent to LKML because we Linux kernel community will take care. Signed-off-by: Minchan Kim <minchan@kernel.org> Cc: Nitin Gupta <ngupta@vflare.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zram: promote zram from stagingMinchan Kim2014-01-301-0/+77
Zram has lived in staging for a LONG LONG time and have been fixed/improved by many contributors so code is clean and stable now. Of course, there are lots of product using zram in real practice. The major TV companys have used zram as swap since two years ago and recently our production team released android smart phone with zram which is used as swap, too and recently Android Kitkat start to use zram for small memory smart phone. And there was a report Google released their ChromeOS with zram, too and cyanogenmod have been used zram long time ago. And I heard some disto have used zram block device for tmpfs. In addition, I saw many report from many other peoples. For example, Lubuntu start to use it. The benefit of zram is very clear. With my experience, one of the benefit was to remove jitter of video application with backgroud memory pressure. It would be effect of efficient memory usage by compression but more issue is whether swap is there or not in the system. Recent mobile platforms have used JAVA so there are many anonymous pages. But embedded system normally are reluctant to use eMMC or SDCard as swap because there is wear-leveling and latency issues so if we do not use swap, it means we can't reclaim anoymous pages and at last, we could encounter OOM kill. :( Although we have real storage as swap, it was a problem, too. Because it sometime ends up making system very unresponsible caused by slow swap storage performance. Quote from Luigi on Google "Since Chrome OS was mentioned: the main reason why we don't use swap to a disk (rotating or SSD) is because it doesn't degrade gracefully and leads to a bad interactive experience. Generally we prefer to manage RAM at a higher level, by transparently killing and restarting processes. But we noticed that zram is fast enough to be competitive with the latter, and it lets us make more efficient use of the available RAM. " and he announced. http://www.spinics.net/lists/linux-mm/msg57717.html Other uses case is to use zram for block device. Zram is block device so anyone can format the block device and mount on it so some guys on the internet start zram as /var/tmp. http://forums.gentoo.org/viewtopic-t-838198-start-0.html Let's promote zram and enhance/maintain it instead of removing. Signed-off-by: Minchan Kim <minchan@kernel.org> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Acked-by: Nitin Gupta <ngupta@vflare.org> Acked-by: Pekka Enberg <penberg@kernel.org> Cc: Bob Liu <bob.liu@oracle.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Hugh Dickins <hughd@google.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: Luigi Semenzato <semenzato@google.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Rik van Riel <riel@redhat.com> Cc: Seth Jennings <sjenning@linux.vnet.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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