The patch titled
Subject: mm, slab, vmscan: accumulate gradual pressure on small slabs
has been added to the -mm tree. Its filename is
mmslabvmscan-accumulate-gradual-pressure-on-small-slabs.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mmslabvmscan-accumulate-gradual-pressure-on-small-slabs.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mmslabvmscan-accumulate-gradual-pressure-on-small-slabs.patch
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From: Rik van Riel <riel@xxxxxxxxxxx>
Subject: mm, slab, vmscan: accumulate gradual pressure on small slabs
There are a few issues with the way the number of slab objects to scan is
calculated in do_shrink_slab. First, for zero-seek slabs, we could leave
the last object around forever. That could result in pinning a dying
cgroup into memory, instead of reclaiming it. The fix for that is
trivial.
Secondly, small slabs receive much more pressure, relative to their size,
than larger slabs, due to "rounding up" the minimum number of scanned
objects to batch_size.
We can keep the pressure on all slabs equal relative to their size by
accumulating the scan pressure on small slabs over time, resulting in
sometimes scanning an object, instead of always scanning several.
This results in lower system CPU use, and a lower major fault rate, as
actively used entries from smaller caches get reclaimed less aggressively,
and need to be reloaded/recreated less often.
Link: http://lkml.kernel.org/r/20190128143535.7767c397@xxxxxxxxxxxxxxxxxxxx
Fixes: 4b85afbdacd2 ("mm: zero-seek shrinkers")
Fixes: 172b06c32b94 ("mm: slowly shrink slabs with a relatively small number of objects")
Signed-off-by: Rik van Riel <riel@xxxxxxxxxxx>
Tested-by: Chris Mason <clm@xxxxxx>
Acked-by: Roman Gushchin <guro@xxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Chris Mason <clm@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/shrinker.h | 1 +
mm/vmscan.c | 16 +++++++++++++---
2 files changed, 14 insertions(+), 3 deletions(-)
--- a/include/linux/shrinker.h~mmslabvmscan-accumulate-gradual-pressure-on-small-slabs
+++ a/include/linux/shrinker.h
@@ -65,6 +65,7 @@ struct shrinker {
long batch; /* reclaim batch size, 0 = default */
int seeks; /* seeks to recreate an obj */
+ int small_scan; /* accumulate pressure on slabs with few objects */
unsigned flags;
/* These are for internal use */
--- a/mm/vmscan.c~mmslabvmscan-accumulate-gradual-pressure-on-small-slabs
+++ a/mm/vmscan.c
@@ -488,18 +488,28 @@ static unsigned long do_shrink_slab(stru
* them aggressively under memory pressure to keep
* them from causing refetches in the IO caches.
*/
- delta = freeable / 2;
+ delta = (freeable + 1)/ 2;
}
/*
* Make sure we apply some minimal pressure on default priority
- * even on small cgroups. Stale objects are not only consuming memory
+ * even on small cgroups, by accumulating pressure across multiple
+ * slab shrinker runs. 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));
+ if (!delta) {
+ shrinker->small_scan += freeable;
+
+ delta = shrinker->small_scan >> priority;
+ shrinker->small_scan -= delta << priority;
+
+ delta *= 4;
+ do_div(delta, shrinker->seeks);
+
+ }
total_scan += delta;
if (total_scan < 0) {
_
Patches currently in -mm which might be from riel@xxxxxxxxxxx are
mmslabvmscan-accumulate-gradual-pressure-on-small-slabs.patch
