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[PATCH 020/102] xfs: warn if direct reclaim tries to writeback pages

To: xfs@xxxxxxxxxxx
Subject: [PATCH 020/102] xfs: warn if direct reclaim tries to writeback pages
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Thu, 23 Aug 2012 15:01:38 +1000
In-reply-to: <1345698180-13612-1-git-send-email-david@xxxxxxxxxxxxx>
References: <1345698180-13612-1-git-send-email-david@xxxxxxxxxxxxx>
From: Mel Gorman <mgorman@xxxxxxx>

Upstream commit: 94054fa3fca1fd78db02cb3d68d5627120f0a1d4

Direct reclaim should never writeback pages.  For now, handle the
situation and warn about it.  Ultimately, this will be a BUG_ON.

Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Johannes Weiner <jweiner@xxxxxxxxxx>
Cc: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Minchan Kim <minchan.kim@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Alex Elder <aelder@xxxxxxx>
Cc: Theodore Ts'o <tytso@xxxxxxx>
Cc: Chris Mason <chris.mason@xxxxxxxxxx>
Cc: Dave Hansen <dave@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
---
 fs/xfs/linux-2.6/xfs_aops.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/xfs/linux-2.6/xfs_aops.c b/fs/xfs/linux-2.6/xfs_aops.c
index f16207b..4ff2404 100644
--- a/fs/xfs/linux-2.6/xfs_aops.c
+++ b/fs/xfs/linux-2.6/xfs_aops.c
@@ -943,11 +943,11 @@ xfs_vm_writepage(
         * random callers for direct reclaim or memcg reclaim.  We explicitly
         * allow reclaim from kswapd as the stack usage there is relatively low.
         *
-        * This should really be done by the core VM, but until that happens
-        * filesystems like XFS, btrfs and ext4 have to take care of this
-        * by themselves.
+        * This should never happen except in the case of a VM regression so
+        * warn about it.
         */
-       if ((current->flags & (PF_MEMALLOC|PF_KSWAPD)) == PF_MEMALLOC)
+       if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) ==
+                       PF_MEMALLOC))
                goto redirty;
 
        /*
-- 
1.7.10

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