[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>

2 files changed, 1 insertions, 3 deletions

diff --git a/mm/truncate.c b/mm/truncate.c
index 7dee32745901..b1a463d0fe71 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -249,7 +249,6 @@ unlock:
                                 break;
                 }
                 pagevec_release(&pvec);
-                cond_resched();
         }
         return ret;
 }
diff --git a/mm/vmscan.c b/mm/vmscan.c
index be8235fb1939..428c5801d4b4 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -180,8 +180,7 @@ EXPORT_SYMBOL(remove_shrinker);
  *
  * Returns the number of slab objects which we shrunk.
  */
-static int shrink_slab(unsigned long scanned, gfp_t gfp_mask,
-                        unsigned long lru_pages)
+int shrink_slab(unsigned long scanned, gfp_t gfp_mask, unsigned long lru_pages)
 {
         struct shrinker *shrinker;
         int ret = 0;