Re: [PATCH] vmscan: skip freeing memory from zones with lots free

Andrew Morton
2008-11-29T17:45:37Z

On Sat, 29 Nov 2008 11:47:25 -0500 Rik van Riel <riel@redhat.com> wrote:

> Andrew Morton wrote:
>
> >> Index: linux-2.6.28-rc5/mm/vmscan.c
> >> ===================================================================
> >> --- linux-2.6.28-rc5.orig/mm/vmscan.c 2008-11-28 05:53:56.000000000 -0500
> >> +++ linux-2.6.28-rc5/mm/vmscan.c 2008-11-28 06:05:29.000000000 -0500
> >> @@ -1510,6 +1510,9 @@ static unsigned long shrink_zones(int pr
> >> if (zone_is_all_unreclaimable(zone) &&
> >> priority != DEF_PRIORITY)
> >> continue; /* Let kswapd poll it */
> >> + if (zone_watermark_ok(zone, sc->order,
> >> + 4*zone->pages_high, high_zoneidx, 0))
> >> + continue; /* Lots free already */
> >> sc->all_unreclaimable = 0;
> >> } else {
> >> /*
> >
> > We already tried this, or something very similar in effect, I think...
>
> Yes, we have a check just like this in balance_pgdat().
>
> It's been there forever with no ill effect.

This patch affects direct reclaim as well as kswapd.

> > commit 26e4931632352e3c95a61edac22d12ebb72038fe
> > Author: akpm <akpm>
> > Date: Sun Sep 8 19:21:55 2002 +0000
> >
> > [PATCH] refill the inactive list more quickly
> >
> > Fix a problem noticed by Ed Tomlinson: under shifting workloads the
> > shrink_zone() logic will refill the inactive load too slowly.
> >
> > Bale out of the zone scan when we've reclaimed enough pages. Fixes a
> > rarely-occurring problem wherein refill_inactive_zone() ends up
> > shuffling 100,000 pages and generally goes silly.
>
> This is not a bale out, this is a "skip zones that have way
> too many free pages already".

It is similar in effect.

Will this new patch reintroduce the problem which
26e4931632352e3c95a61edac22d12ebb72038fe fixed?