linux-kernel - Re: [patch] mm: vmscan implement per-zone shrinkers

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Date:	Mon, 15 Nov 2010 09:50:36 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	kosaki.motohiro@...fujitsu.com, Nick Piggin <npiggin@...nel.dk>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [patch] mm: vmscan implement per-zone shrinkers

> > @@ -1835,8 +1978,6 @@ static void shrink_zone(int priority, st
> >  			break;
> >  	}
> >  
> > -	sc->nr_reclaimed = nr_reclaimed;
> > -
> >  	/*
> >  	 * Even if we did not try to evict anon pages at all, we want to
> >  	 * rebalance the anon lru active/inactive ratio.
> > @@ -1844,6 +1985,23 @@ static void shrink_zone(int priority, st
> >  	if (inactive_anon_is_low(zone, sc))
> >  		shrink_active_list(SWAP_CLUSTER_MAX, zone, sc, priority, 0);
> >  
> > +	/*
> > +	 * Don't shrink slabs when reclaiming memory from
> > +	 * over limit cgroups
> > +	 */
> > +	if (sc->may_reclaim_slab) {
> > +		struct reclaim_state *reclaim_state = current->reclaim_state;
> > +
> > +		shrink_slab(zone, sc->nr_scanned - nr_scanned,
> 
> Doubtful calculation. What mean "sc->nr_scanned - nr_scanned"?
> I think nr_scanned simply keep old slab balancing behavior.

And per-zone reclaim can lead to new issue. On 32bit highmem system,
theorically the system has following memory usage.

ZONE_HIGHMEM: 100% used for page cache
ZONE_NORMAL:  100% used for slab

So, traditional page-cache/slab balancing may not work. I think following
new calculation or somethinhg else is necessary.

	if (zone_reclaimable_pages() > NR_SLAB_RECLAIMABLE) {
		using current calculation
	} else {
		shrink number of "objects >> reclaim-priority" objects
		(as page cache scanning calculation)
	}

However, it can be separate this patch, perhaps.



> 
> 
> > +			lru_pages, global_lru_pages, sc->gfp_mask);
> > +		if (reclaim_state) {
> > +			nr_reclaimed += reclaim_state->reclaimed_slab;
> > +			reclaim_state->reclaimed_slab = 0;
> > +		}
> > +	}
> > +
> > +	sc->nr_reclaimed = nr_reclaimed;
> > +
> >  	throttle_vm_writeout(sc->gfp_mask);
> >  }


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