[PATCH][5/?] count writeback pages in nr_scanned

[Rik van Riel]

Still untested, but posting the concept here anyway, since this
could explain a lot...

OOM kills have been observed with 70% of the pages in lowmem being
in the writeback state.  If we count those pages in sc->nr_scanned,
the VM should throttle and wait for IO completion, instead of OOM
killing.

Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>

--- linux-2.6.9/mm/vmscan.c.screclaim	2005-01-03 12:17:56.547148905 -0500
+++ linux-2.6.9/mm/vmscan.c	2005-01-03 12:18:16.855965416 -0500
@@ -376,10 +376,10 @@

 		BUG_ON(PageActive(page));

+		sc->nr_scanned++;
 		if (PageWriteback(page))
 			goto keep_locked;

-		sc->nr_scanned++;
 		/* Double the slab pressure for mapped and swapcache pages */
 		if (page_mapped(page) || PageSwapCache(page))
 			sc->nr_scanned++;
-
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