linux-kernel - [PATCH] [34/99] UBIFS: fix shrinker object count reports

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Message-Id: <20110727214832.E64A02403FF@tassilo.jf.intel.com>
Date:	Wed, 27 Jul 2011 14:48:32 -0700 (PDT)
From:	Andi Kleen <andi@...stfloor.org>
To:	Artem.Bityutskiy@...ia.com, gregkh@...e.de, ak@...ux.intel.com,
	linux-kernel@...r.kernel.org, stable@...nel.org,
	tim.bird@...sony.com
Subject: [PATCH] [34/99] UBIFS: fix shrinker object count reports

2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: Artem Bityutskiy <Artem.Bityutskiy@...ia.com>

commit cf610bf4199770420629d3bc273494bd27ad6c1d upstream.

Sometimes VM asks the shrinker to return amount of objects it can shrink,
and we return the ubifs_clean_zn_cnt in that case. However, it is possible
that this counter is negative for a short period of time, due to the way
UBIFS TNC code updates it. And I can observe the following warnings sometimes:

shrink_slab: ubifs_shrinker+0x0/0x2b7 [ubifs] negative objects to delete nr=-8541616642706119788

This patch makes sure UBIFS never returns negative count of objects.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@...ia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
Signed-off-by: Andi Kleen <ak@...ux.intel.com>

---
 fs/ubifs/shrinker.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

Index: linux-2.6.35.y/fs/ubifs/shrinker.c
===================================================================
--- linux-2.6.35.y.orig/fs/ubifs/shrinker.c
+++ linux-2.6.35.y/fs/ubifs/shrinker.c
@@ -283,7 +283,11 @@ int ubifs_shrinker(struct shrinker *shri
 	long clean_zn_cnt = atomic_long_read(&ubifs_clean_zn_cnt);
 
 	if (nr == 0)
-		return clean_zn_cnt;
+		/*
+		 * Due to the way UBIFS updates the clean znode counter it may
+		 * temporarily be negative.
+		 */
+		return clean_zn_cnt >= 0 ? clean_zn_cnt : 1;
 
 	if (!clean_zn_cnt) {
 		/*
--
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