linux-kernel - [PATCH] mm: fix warning in __set_page_dirty

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Date:	Sat, 2 Jun 2012 00:27:47 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	Dave Jones <davej@...hat.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Mel Gorman <mgorman@...e.de>, Minchan Kim <minchan@...nel.org>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Cong Wang <amwang@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: [PATCH] mm: fix warning in __set_page_dirty_nobuffers

New tmpfs use of !PageUptodate pages for fallocate() is triggering the
WARNING: at mm/page-writeback.c:1990 when __set_page_dirty_nobuffers()
is called from migrate_page_copy() for compaction.

It is anomalous that migration should use __set_page_dirty_nobuffers()
on an address_space that does not participate in dirty and writeback
accounting; and this has also been observed to insert surprising dirty
tags into a tmpfs radix_tree, despite tmpfs not using tags at all.

We should probably give migrate_page_copy() a better way to preserve
the tag and migrate accounting info, when mapping_cap_account_dirty().
But that needs some more work: so in the interim, avoid the warning
by using a simple SetPageDirty on PageSwapBacked pages.

Reported-by: Dave Jones <davej@...hat.com>
Signed-off-by: Hugh Dickins <hughd@...gle.com>
---

 mm/migrate.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- 3.4.0+/mm/migrate.c	2012-05-27 10:01:43.104049010 -0700
+++ linux/mm/migrate.c	2012-06-01 00:10:58.080098749 -0700
@@ -436,7 +436,10 @@ void migrate_page_copy(struct page *newp
 		 * is actually a signal that all of the page has become dirty.
 		 * Whereas only part of our page may be dirty.
 		 */
-		__set_page_dirty_nobuffers(newpage);
+		if (PageSwapBacked(page))
+			SetPageDirty(newpage);
+		else
+			__set_page_dirty_nobuffers(newpage);
  	}

 	mlock_migrate_page(newpage, page);
--
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