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

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Date:	Thu, 21 Jul 2011 17:28:44 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Linux-MM <linux-mm@...ck.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, XFS <xfs@....sgi.com>,
	Dave Chinner <david@...morbit.com>,
	Christoph Hellwig <hch@...radead.org>,
	Johannes Weiner <jweiner@...hat.com>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Mel Gorman <mgorman@...e.de>
Subject: [PATCH 2/8] xfs: Warn if direct reclaim tries to writeback pages

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@...e.de>
---
 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
-- 
1.7.3.4

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