summaryrefslogtreecommitdiffstats
diff options
context:
space:
mode:
-rw-r--r--Documentation/sysctl/vm.txt33
-rw-r--r--fs/drop_caches.c16
-rw-r--r--include/linux/vm_event_item.h1
-rw-r--r--kernel/sysctl.c4
-rw-r--r--mm/vmstat.c3
5 files changed, 47 insertions, 10 deletions
diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index d614a9b..dd9d0e3 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -175,18 +175,39 @@ Setting this to zero disables periodic writeback altogether.
drop_caches
-Writing to this will cause the kernel to drop clean caches, dentries and
-inodes from memory, causing that memory to become free.
+Writing to this will cause the kernel to drop clean caches, as well as
+reclaimable slab objects like dentries and inodes. Once dropped, their
+memory becomes free.
To free pagecache:
echo 1 > /proc/sys/vm/drop_caches
-To free dentries and inodes:
+To free reclaimable slab objects (includes dentries and inodes):
echo 2 > /proc/sys/vm/drop_caches
-To free pagecache, dentries and inodes:
+To free slab objects and pagecache:
echo 3 > /proc/sys/vm/drop_caches
-As this is a non-destructive operation and dirty objects are not freeable, the
-user should run `sync' first.
+This is a non-destructive operation and will not free any dirty objects.
+To increase the number of objects freed by this operation, the user may run
+`sync' prior to writing to /proc/sys/vm/drop_caches. This will minimize the
+number of dirty objects on the system and create more candidates to be
+dropped.
+
+This file is not a means to control the growth of the various kernel caches
+(inodes, dentries, pagecache, etc...) These objects are automatically
+reclaimed by the kernel when memory is needed elsewhere on the system.
+
+Use of this file can cause performance problems. Since it discards cached
+objects, it may cost a significant amount of I/O and CPU to recreate the
+dropped objects, especially if they were under heavy use. Because of this,
+use outside of a testing or debugging environment is not recommended.
+
+You may see informational messages in your kernel log when this file is
+used:
+
+ cat (1234): drop_caches: 3
+
+These are informational only. They do not mean that anything is wrong
+with your system. To disable them, echo 4 (bit 3) into drop_caches.
==============================================================
diff --git a/fs/drop_caches.c b/fs/drop_caches.c
index 9fd702f..9280202 100644
--- a/fs/drop_caches.c
+++ b/fs/drop_caches.c
@@ -59,10 +59,22 @@ int drop_caches_sysctl_handler(ctl_table *table, int write,
if (ret)
return ret;
if (write) {
- if (sysctl_drop_caches & 1)
+ static int stfu;
+
+ if (sysctl_drop_caches & 1) {
iterate_supers(drop_pagecache_sb, NULL);
- if (sysctl_drop_caches & 2)
+ count_vm_event(DROP_PAGECACHE);
+ }
+ if (sysctl_drop_caches & 2) {
drop_slab();
+ count_vm_event(DROP_SLAB);
+ }
+ if (!stfu) {
+ pr_info("%s (%d): drop_caches: %d\n",
+ current->comm, task_pid_nr(current),
+ sysctl_drop_caches);
+ }
+ stfu |= sysctl_drop_caches & 4;
}
return 0;
}
diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 3a712e2..486c397 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -37,6 +37,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
PGINODESTEAL, SLABS_SCANNED, KSWAPD_INODESTEAL,
KSWAPD_LOW_WMARK_HIT_QUICKLY, KSWAPD_HIGH_WMARK_HIT_QUICKLY,
PAGEOUTRUN, ALLOCSTALL, PGROTATED,
+ DROP_PAGECACHE, DROP_SLAB,
#ifdef CONFIG_NUMA_BALANCING
NUMA_PTE_UPDATES,
NUMA_HUGE_PTE_UPDATES,
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 09d2e24..5c14b54 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -123,7 +123,7 @@ static int __maybe_unused neg_one = -1;
static int zero;
static int __maybe_unused one = 1;
static int __maybe_unused two = 2;
-static int __maybe_unused three = 3;
+static int __maybe_unused four = 4;
static unsigned long one_ul = 1;
static int one_hundred = 100;
#ifdef CONFIG_PRINTK
@@ -1264,7 +1264,7 @@ static struct ctl_table vm_table[] = {
.mode = 0644,
.proc_handler = drop_caches_sysctl_handler,
.extra1 = &one,
- .extra2 = &three,
+ .extra2 = &four,
},
#ifdef CONFIG_COMPACTION
{
diff --git a/mm/vmstat.c b/mm/vmstat.c
index f3155d5..197b4c4 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -813,6 +813,9 @@ const char * const vmstat_text[] = {
"pgrotated",
+ "drop_pagecache",
+ "drop_slab",
+
#ifdef CONFIG_NUMA_BALANCING
"numa_pte_updates",
"numa_huge_pte_updates",
OpenPOWER on IntegriCloud