Revert "mm: slowly shrink slabs with a relatively small number of objects"

This reverts commit 172b06c32b9497 ("mm: slowly shrink slabs with a
relatively small number of objects").

This change changes the agressiveness of shrinker reclaim, causing small
cache and low priority reclaim to greatly increase scanning pressure on
small caches.  As a result, light memory pressure has a disproportionate
affect on small caches, and causes large caches to be reclaimed much
faster than previously.

As a result, it greatly perturbs the delicate balance of the VFS caches
(dentry/inode vs file page cache) such that the inode/dentry caches are
reclaimed much, much faster than the page cache and this drives us into
several other caching imbalance related problems.

As such, this is a bad change and needs to be reverted.

[ Needs some massaging to retain the later seekless shrinker
  modifications.]

Link: http://lkml.kernel.org/r/20190130041707.27750-3-david@fromorbit.com
Fixes: 172b06c32b9497 ("mm: slowly shrink slabs with a relatively small number of objects")
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Cc: Wolfgang Walter <linux@stwm.de>
Cc: Roman Gushchin <guro@fb.com>
Cc: Spock <dairinin@gmail.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index a714c4f..e979705 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -491,16 +491,6 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
                delta = freeable / 2;
        }
 
-       /*
-        * Make sure we apply some minimal pressure on default priority
-        * even on small cgroups. Stale objects are not only consuming memory
-        * by themselves, but can also hold a reference to a dying cgroup,
-        * preventing it from being reclaimed. A dying cgroup with all
-        * corresponding structures like per-cpu stats and kmem caches
-        * can be really big, so it may lead to a significant waste of memory.
-        */
-       delta = max_t(unsigned long long, delta, min(freeable, batch_size));
-
        total_scan += delta;
        if (total_scan < 0) {
                pr_err("shrink_slab: %pF negative objects to delete nr=%ld\n",