linux-kernel - Re: 2.6.26-rc: nfsd hangs for a few sec

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Message-ID: <20080622013801.GE4692@csn.ul.ie>
Date:	Sun, 22 Jun 2008 02:38:02 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Christoph Lameter <clameter@....com>
Cc:	Alexander Beregalov <a.beregalov@...il.com>,
	kernel-testers@...r.kernel.org,
	kernel list <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
	Lee Schermerhorn <lee.schermerhorn@...com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Hugh Dickins <hugh@...itas.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	bfields@...ldses.org, neilb@...e.de, linux-nfs@...r.kernel.org
Subject: Re: 2.6.26-rc: nfsd hangs for a few sec

On (21/06/08 17:18), Christoph Lameter didst pronounce:
> On Sat, 21 Jun 2008, Mel Gorman wrote:
> 
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -1249,15 +1249,13 @@ static unsigned long shrink_zone(int priority, struct zone *zone,
> >  static unsigned long shrink_zones(int priority, struct zonelist *zonelist,
> >  					struct scan_control *sc)
> >  {
> > +	enum zone_type high_zoneidx = gfp_zone(sc->gfp_mask);
> >  	unsigned long nr_reclaimed = 0;
> > -	struct zone **zones = zonelist->zones;
> > -	int i;
> > -
> > +	struct zone **z;
> > +	struct zone *zone;
> >  
> >  	sc->all_unreclaimable = 1;
> > -	for (i = 0; zones[i] != NULL; i++) {
> > -		struct zone *zone = zones[i];
> > -
> > +	for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) {
> >  		if (!populated_zone(zone))
> >  			continue;
> >  		/*
> > 
> > Code before - Walk the zonelist for GFP_KERNEL
> 
> Before the change we walk all zones of the zonelist.
> 

Yeah, but the zonelist is for GFP_KERNEL so it should not include the HIGHMEM
zones, right? The key change is that after the patch there are fewer zonelists
than get filtered.

> > Code after - Filter zonelist based on what is allowed for GFP_KERNEL
> 
> After the change we walk only zones for GFP_KERNEL. Meaning no HIGHMEM 
> and MOVABLE zones. Doesnt that mean that reclaim is limited to ZONE_DMA 
> and ZONE_NORMAL? Is that really intended?
> 

It is for GFP_KERNEL allocations but that is expected.

> If not then the following patch should return us to old behavior:
> 

I think the effect of that patch is that zones get shrunk that have
nothing to do with the requestors requirements. Right?

> ---
>  mm/vmscan.c |    3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> Index: linux-2.6/mm/vmscan.c
> ===================================================================
> --- linux-2.6.orig/mm/vmscan.c	2008-06-21 17:15:45.597627317 -0700
> +++ linux-2.6/mm/vmscan.c	2008-06-21 17:17:16.273293260 -0700
> @@ -1249,13 +1249,12 @@ static unsigned long shrink_zone(int pri
>  static unsigned long shrink_zones(int priority, struct zonelist *zonelist,
>  					struct scan_control *sc)
>  {
> -	enum zone_type high_zoneidx = gfp_zone(sc->gfp_mask);
>  	unsigned long nr_reclaimed = 0;
>  	struct zoneref *z;
>  	struct zone *zone;
>  
>  	sc->all_unreclaimable = 1;
> -	for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) {
> +	for_each_zone_zonelist(zone, z, zonelist, MAX_NR_ZONES - 1) {
>  		if (!populated_zone(zone))
>  			continue;
>  		/*
> 

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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