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[PATCH 3/7] xfs: Warn if direct reclaim tries to writeback pages

To: Linux-MM <linux-mm@xxxxxxxxx>
Subject: [PATCH 3/7] xfs: Warn if direct reclaim tries to writeback pages
From: Mel Gorman <mgorman@xxxxxxx>
Date: Wed, 10 Aug 2011 11:47:16 +0100
Cc: LKML <linux-kernel@xxxxxxxxxxxxxxx>, XFS <xfs@xxxxxxxxxxx>, Dave Chinner <david@xxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, Johannes Weiner <jweiner@xxxxxxxxxx>, Wu Fengguang <fengguang.wu@xxxxxxxxx>, Jan Kara <jack@xxxxxxx>, Rik van Riel <riel@xxxxxxxxxx>, Minchan Kim <minchan.kim@xxxxxxxxx>, Mel Gorman <mgorman@xxxxxxx>
In-reply-to: <1312973240-32576-1-git-send-email-mgorman@xxxxxxx>
References: <1312973240-32576-1-git-send-email-mgorman@xxxxxxx>
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>
---
 fs/xfs/linux-2.6/xfs_aops.c |    7 +++----
 1 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/fs/xfs/linux-2.6/xfs_aops.c b/fs/xfs/linux-2.6/xfs_aops.c
index 79ce38b..afea9cd 100644
--- a/fs/xfs/linux-2.6/xfs_aops.c
+++ b/fs/xfs/linux-2.6/xfs_aops.c
@@ -930,11 +930,10 @@ 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;
 
        /*
-- 
1.7.3.4

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