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[PATCH 2/8] xfs: Warn if direct reclaim tries to writeback pages

To: Linux-MM <linux-mm@xxxxxxxxx>
Subject: [PATCH 2/8] xfs: Warn if direct reclaim tries to writeback pages
From: Mel Gorman <mgorman@xxxxxxx>
Date: Thu, 21 Jul 2011 17:28:44 +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: <1311265730-5324-1-git-send-email-mgorman@xxxxxxx>
References: <1311265730-5324-1-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 |    9 +++++----
 1 files changed, 5 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..c33a439 100644
--- a/fs/xfs/linux-2.6/xfs_aops.c
+++ b/fs/xfs/linux-2.6/xfs_aops.c
@@ -930,12 +930,13 @@ 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 ((current->flags & (PF_MEMALLOC|PF_KSWAPD)) == PF_MEMALLOC) {
+               WARN_ON_ONCE(1);
                goto redirty;
+       }
         * We need a transaction if there are delalloc or unwritten buffers

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