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

[Dave Chinner]

From: Mel Gorman <mgorman at suse.de>

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 at suse.de>
Cc: Dave Chinner <david at fromorbit.com>
Cc: Christoph Hellwig <hch at infradead.org>
Cc: Johannes Weiner <jweiner at redhat.com>
Cc: Wu Fengguang <fengguang.wu at intel.com>
Cc: Jan Kara <jack at suse.cz>
Cc: Minchan Kim <minchan.kim at gmail.com>
Cc: Rik van Riel <riel at redhat.com>
Cc: Mel Gorman <mgorman at suse.de>
Cc: Alex Elder <aelder at sgi.com>
Cc: Theodore Ts'o <tytso at mit.edu>
Cc: Chris Mason <chris.mason at oracle.com>
Cc: Dave Hansen <dave at linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
---
 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