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

[Andrew Morton <akpm@osdl.org>]

Rik van Riel <riel@redhat.com> wrote:
>
> 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@redhat.com>
> 
>  --- 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++;

Patch looks very sane.  It in fact restores that which we were doing until
12 June 2004, when the rampant `struct scan_control' depredations violated
the tree.