From 896e91a9dc4b3d238f30638da88dcda132dddaf3 Mon Sep 17 00:00:00 2001
From: Hugh Dickins <hughd@google.com>
Date: Tue, 31 Jul 2012 16:45:59 -0700
Subject: [PATCH] --- yaml --- r: 320858 b: refs/heads/master c:
 c3b94f44fcb0725471ecebb701c077a0ed67bd07 h: refs/heads/master v: v3

---
 [refs]            |  2 +-
 trunk/mm/vmscan.c | 33 ++++++++++++++++++++++++---------
 2 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/[refs] b/[refs]
index fed31f09f558..20de2f6d6dee 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: e62e384e9da8d9a0c599795464a7e76fd490931c
+refs/heads/master: c3b94f44fcb0725471ecebb701c077a0ed67bd07
diff --git a/trunk/mm/vmscan.c b/trunk/mm/vmscan.c
index ca43aa00ea0e..e37e68725090 100644
--- a/trunk/mm/vmscan.c
+++ b/trunk/mm/vmscan.c
@@ -723,23 +723,38 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 			/*
 			 * memcg doesn't have any dirty pages throttling so we
 			 * could easily OOM just because too many pages are in
-			 * writeback from reclaim and there is nothing else to
-			 * reclaim.
+			 * writeback and there is nothing else to reclaim.
 			 *
-			 * Check may_enter_fs, certainly because a loop driver
+			 * Check __GFP_IO, certainly because a loop driver
 			 * thread might enter reclaim, and deadlock if it waits
 			 * on a page for which it is needed to do the write
 			 * (loop masks off __GFP_IO|__GFP_FS for this reason);
 			 * but more thought would probably show more reasons.
+			 *
+			 * Don't require __GFP_FS, since we're not going into
+			 * the FS, just waiting on its writeback completion.
+			 * Worryingly, ext4 gfs2 and xfs allocate pages with
+			 * grab_cache_page_write_begin(,,AOP_FLAG_NOFS), so
+			 * testing may_enter_fs here is liable to OOM on them.
 			 */
-			if (!global_reclaim(sc) && PageReclaim(page) &&
-					may_enter_fs)
-				wait_on_page_writeback(page);
-			else {
+			if (global_reclaim(sc) ||
+			    !PageReclaim(page) || !(sc->gfp_mask & __GFP_IO)) {
+				/*
+				 * This is slightly racy - end_page_writeback()
+				 * might have just cleared PageReclaim, then
+				 * setting PageReclaim here end up interpreted
+				 * as PageReadahead - but that does not matter
+				 * enough to care.  What we do want is for this
+				 * page to have PageReclaim set next time memcg
+				 * reclaim reaches the tests above, so it will
+				 * then wait_on_page_writeback() to avoid OOM;
+				 * and it's also appropriate in global reclaim.
+				 */
+				SetPageReclaim(page);
 				nr_writeback++;
-				unlock_page(page);
-				goto keep;
+				goto keep_locked;
 			}
+			wait_on_page_writeback(page);
 		}
 
 		references = page_check_references(page, sc);