linux-kernel - Re: [PATCH 08/10] mm: vmscan: Have kswapd shrink slab only once per priority

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Date:	Wed, 10 Apr 2013 14:23:25 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Dave Chinner <david@...morbit.com>
Cc:	Mel Gorman <mgorman@...e.de>, Linux-MM <linux-mm@...ck.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	Rik van Riel <riel@...hat.com>,
	Zlatko Calusic <zcalusic@...sync.net>,
	Johannes Weiner <hannes@...xchg.org>,
	dormando <dormando@...ia.net>,
	Satoru Moriya <satoru.moriya@....com>,
	Michal Hocko <mhocko@...e.cz>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 08/10] mm: vmscan: Have kswapd shrink slab only once per
 priority

Hello, Dave.

On Wed, Apr 10, 2013 at 11:07:34AM +1000, Dave Chinner wrote:
> On Tue, Apr 09, 2013 at 12:13:59PM +0100, Mel Gorman wrote:
> > On Tue, Apr 09, 2013 at 03:53:25PM +0900, Joonsoo Kim wrote:
> > 
> > > I think that outside of zone loop is better place to run shrink_slab(),
> > > because shrink_slab() is not directly related to a specific zone.
> > > 
> > 
> > This is true and has been the case for a long time. The slab shrinkers
> > are not zone aware and it is complicated by the fact that slab usage can
> > indirectly pin memory on other zones.
> ......
> > > And this is a question not related to this patch.
> > > Why nr_slab is used here to decide zone->all_unreclaimable?
> > 
> > Slab is not directly associated with a slab but as reclaiming slab can
> > free memory from unpredictable zones we do not consider a zone to be
> > fully unreclaimable until we cannot shrink slab any more.
> 
> This is something the numa aware shrinkers will greatly help with -
> instead of being a global shrink it becomes a
> node-the-zone-belongs-to shrink, and so....
> 
> > You may be thinking that this is extremely heavy handed and you're
> > right, it is.
> 
> ... it is much less heavy handed than the current code...
> 
> > > nr_slab is not directly related whether a specific zone is reclaimable
> > > or not, and, moreover, nr_slab is not directly related to number of
> > > reclaimed pages. It just say some objects in the system are freed.
> > > 
> > 
> > All true, it's the indirect relation between slab objects and the memory
> > that is freed when slab objects are reclaimed that has to be taken into
> > account.
> 
> Node awareness within the shrinker infrastructure and LRUs make the
> relationship much more direct ;)

Yes, I think so ;)

Thanks.

> 
> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@...morbit.com
> 
> --
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