The patch titled
Subject: mm/vmscan.c: set correct defer count for shrinker
has been added to the -mm tree. Its filename is
vmscan-set-correct-defer-count-for-shrinker.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/vmscan-set-correct-defer-count-for-shrinker.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/vmscan-set-correct-defer-count-for-shrinker.patch
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From: Shaohua Li <shli@xxxxxx>
Subject: mm/vmscan.c: set correct defer count for shrinker
Our system uses significantly more slab memory with memcg enabled with the
latest kernel. With 3.10 kernel, slab uses 2G memory, while with 4.6
kernel, 6G memory is used. The shrinker has problem. Let's see we have
two memcg for one shrinker. In do_shrink_slab:
1. Check cg1. nr_deferred = 0, assume total_scan = 700. batch size
is 1024, then no memory is freed. nr_deferred = 700
2. Check cg2. nr_deferred = 700. Assume freeable = 20, then
total_scan = 10 or 40. Let's assume it's 10. No memory is freed.
nr_deferred = 10.
The deferred share of cg1 is lost in this case. kswapd will free no
memory even run above steps again and again.
The fix makes sure one memcg's deferred share isn't lost.
Link: http://lkml.kernel.org/r/2414be961b5d25892060315fbb56bb19d81d0c07.1476227351.git.shli@xxxxxx
Signed-off-by: Shaohua Li <shli@xxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [4.0+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)
diff -puN mm/vmscan.c~vmscan-set-correct-defer-count-for-shrinker mm/vmscan.c
--- a/mm/vmscan.c~vmscan-set-correct-defer-count-for-shrinker
+++ a/mm/vmscan.c
@@ -291,6 +291,7 @@ static unsigned long do_shrink_slab(stru
int nid = shrinkctl->nid;
long batch_size = shrinker->batch ? shrinker->batch
: SHRINK_BATCH;
+ long scanned = 0, next_deferred;
freeable = shrinker->count_objects(shrinker, shrinkctl);
if (freeable == 0)
@@ -312,7 +313,9 @@ static unsigned long do_shrink_slab(stru
pr_err("shrink_slab: %pF negative objects to delete nr=%ld\n",
shrinker->scan_objects, total_scan);
total_scan = freeable;
- }
+ next_deferred = nr;
+ } else
+ next_deferred = total_scan;
/*
* We need to avoid excessive windup on filesystem shrinkers
@@ -369,17 +372,22 @@ static unsigned long do_shrink_slab(stru
count_vm_events(SLABS_SCANNED, nr_to_scan);
total_scan -= nr_to_scan;
+ scanned += nr_to_scan;
cond_resched();
}
+ if (next_deferred >= scanned)
+ next_deferred -= scanned;
+ else
+ next_deferred = 0;
/*
* move the unused scan count back into the shrinker in a
* manner that handles concurrent updates. If we exhausted the
* scan, there is no need to do an update.
*/
- if (total_scan > 0)
- new_nr = atomic_long_add_return(total_scan,
+ if (next_deferred > 0)
+ new_nr = atomic_long_add_return(next_deferred,
&shrinker->nr_deferred[nid]);
else
new_nr = atomic_long_read(&shrinker->nr_deferred[nid]);
_
Patches currently in -mm which might be from shli@xxxxxx are
vmscan-set-correct-defer-count-for-shrinker.patch
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