linux-kernel - [PATCH v2] zsmalloc: do not take class lock in zs_shrinker

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Date:	Fri, 17 Jul 2015 20:18:18 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: [PATCH v2] zsmalloc: do not take class lock in zs_shrinker_count()

We can avoid taking class ->lock around zs_can_compact() in
zs_shrinker_count(), because the number that we return back
is outdated in general case, by design. We have different
sources that are able to change class's state right after we
return from zs_can_compact() -- ongoing I/O operations, manually
triggered compaction, or two of them happening simultaneously.

We re-do this calculations during compaction on a per class basis
anyway.

zs_unregister_shrinker() will not return until we have an
active shrinker, so classes won't unexpectedly disappear
while zs_shrinker_count() iterates them.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
---
 mm/zsmalloc.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 1edd8a0..ed64cf5 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -1836,9 +1836,7 @@ static unsigned long zs_shrinker_count(struct shrinker *shrinker,
 		if (class->index != i)
 			continue;

-		spin_lock(&class->lock);
 		pages_to_free += zs_can_compact(class);
-		spin_unlock(&class->lock);
 	}

 	return pages_to_free;
-- 
2.4.6

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