[PATCH] vmscan: count writeback pages in nr_scanned

[PATCH] vmscan: count writeback pages in nr_scanned

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.

(akpm: this is how the code was designed to work - we broke it six months
ago).

Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>