[PATCH] drop-pagecache

Add /proc/sys/vm/drop_caches.  When written to, this will cause the kernel to
discard as much pagecache and/or reclaimable slab objects as it can.  THis
operation requires root permissions.

It won't drop dirty data, so the user should run `sync' first.

Caveats:

a) Holds inode_lock for exorbitant amounts of time.

b) Needs to be taught about NUMA nodes: propagate these all the way through
   so the discarding can be controlled on a per-node basis.

This is a debugging feature: useful for getting consistent results between
filesystem benchmarks.  We could possibly put it under a config option, but
it's less than 300 bytes.

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index a85047bb5739..8dcf6fd5b0f9 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -68,6 +68,7 @@ extern int min_free_kbytes;
 extern int printk_ratelimit_jiffies;
 extern int printk_ratelimit_burst;
 extern int pid_max_min, pid_max_max;
+extern int sysctl_drop_caches;
 
 #if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_X86)
 int unknown_nmi_panic;
@@ -775,6 +776,15 @@ static ctl_table vm_table[] = {
                 .strategy       = &sysctl_intvec,
         },
         {
+                .ctl_name       = VM_DROP_PAGECACHE,
+                .procname       = "drop_caches",
+                .data           = &sysctl_drop_caches,
+                .maxlen         = sizeof(int),
+                .mode           = 0644,
+                .proc_handler   = drop_caches_sysctl_handler,
+                .strategy       = &sysctl_intvec,
+        },
+        {
                 .ctl_name       = VM_MIN_FREE_KBYTES,
                 .procname       = "min_free_kbytes",
                 .data           = &min_free_kbytes,