3.14-stable review patch. If anyone has any objections, please let me know.
------------------
From: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
commit d23da150a37c9fe3cc83dbaf71b3e37fd434ed52 upstream.
We remove the call to grab_super_passive in call to super_cache_count.
This becomes a scalability bottleneck as multiple threads are trying to do
memory reclamation, e.g. when we are doing large amount of file read and
page cache is under pressure. The cached objects quickly got reclaimed
down to 0 and we are aborting the cache_scan() reclaim. But counting
creates a log jam acquiring the sb_lock.
We are holding the shrinker_rwsem which ensures the safety of call to
list_lru_count_node() and s_op->nr_cached_objects. The shrinker is
unregistered now before ->kill_sb() so the operation is safe when we are
doing unmount.
The impact will depend heavily on the machine and the workload but for a
small machine using postmark tuned to use 4xRAM size the results were
3.15.0-rc5 3.15.0-rc5
vanilla shrinker-v1r1
Ops/sec Transactions 21.00 ( 0.00%) 24.00 ( 14.29%)
Ops/sec FilesCreate 39.00 ( 0.00%) 44.00 ( 12.82%)
Ops/sec CreateTransact 10.00 ( 0.00%) 12.00 ( 20.00%)
Ops/sec FilesDeleted 6202.00 ( 0.00%) 6202.00 ( 0.00%)
Ops/sec DeleteTransact 11.00 ( 0.00%) 12.00 ( 9.09%)
Ops/sec DataRead/MB 25.97 ( 0.00%) 29.10 ( 12.05%)
Ops/sec DataWrite/MB 49.99 ( 0.00%) 56.02 ( 12.06%)
ffsb running in a configuration that is meant to simulate a mail server showed
3.15.0-rc5 3.15.0-rc5
vanilla shrinker-v1r1
Ops/sec readall 9402.63 ( 0.00%) 9567.97 ( 1.76%)
Ops/sec create 4695.45 ( 0.00%) 4735.00 ( 0.84%)
Ops/sec delete 173.72 ( 0.00%) 179.83 ( 3.52%)
Ops/sec Transactions 14271.80 ( 0.00%) 14482.81 ( 1.48%)
Ops/sec Read 37.00 ( 0.00%) 37.60 ( 1.62%)
Ops/sec Write 18.20 ( 0.00%) 18.30 ( 0.55%)
Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Tested-by: Yuanhan Liu <yuanhan.liu@xxxxxxxxxxxxxxx>
Cc: Bob Liu <bob.liu@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Acked-by: Rik van Riel <riel@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/super.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
--- a/fs/super.c
+++ b/fs/super.c
@@ -114,9 +114,14 @@ static unsigned long super_cache_count(s
sb = container_of(shrink, struct super_block, s_shrink);
- if (!grab_super_passive(sb))
- return 0;
-
+ /*
+ * Don't call grab_super_passive as it is a potential
+ * scalability bottleneck. The counts could get updated
+ * between super_cache_count and super_cache_scan anyway.
+ * Call to super_cache_count with shrinker_rwsem held
+ * ensures the safety of call to list_lru_count_node() and
+ * s_op->nr_cached_objects().
+ */
if (sb->s_op && sb->s_op->nr_cached_objects)
total_objects = sb->s_op->nr_cached_objects(sb,
sc->nid);
@@ -127,7 +132,6 @@ static unsigned long super_cache_count(s
sc->nid);
total_objects = vfs_pressure_ratio(total_objects);
- drop_super(sb);
return total_objects;
}
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