linux-kernel - Re: [PATCH rc5-mm1 1/3] mm-have-zonelist: fix memcg ooms

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Message-ID: <Pine.LNX.4.64.0803121330260.5209@blonde.site>
Date:	Wed, 12 Mar 2008 13:34:57 +0000 (GMT)
From:	Hugh Dickins <hugh@...itas.com>
To:	Mel Gorman <mel@....ul.ie>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH rc5-mm1 1/3] mm-have-zonelist: fix memcg ooms

On Wed, 12 Mar 2008, Mel Gorman wrote:
> On (11/03/08 21:12), Hugh Dickins didst pronounce:
> > @@ -1454,9 +1453,10 @@ unsigned long try_to_free_mem_cgroup_pag
> >  		.isolate_pages = mem_cgroup_isolate_pages,
> >  	};
> >  	struct zonelist *zonelist;
> > -	int target_zone = gfp_zonelist(GFP_HIGHUSER_MOVABLE);
> >  
> > -	zonelist = &NODE_DATA(numa_node_id())->node_zonelists[target_zone];
> > +	sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
> > +			(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
> > +	zonelist = NODE_DATA(numa_node_id())->node_zonelists;
> 
> While it is clear you are setting the mask to include HIGHMEM-related flags,
> it's not as clear to me why you alter the zonelist as well. target_zone was
> already based on HIGHMEM so what are you fixing there?
> 
> It should still work as ->node_zonelists[0] is a zonelist suitable for node
> fallback as opposed to node_zonelists[1] which is for GFP_THISNODE but
> maybe this was not quite what you intended?
> 
> Probably something obvious that will hit me the second I push send :)

That bit wasn't a fix as such, it just came from not wanting to repeat
GFP_HIGHUSER_MOVABLE in there: after I'd looked at gfp_zonelist, it
appeared to be redundant in this context, so I preferred to cut out
the target_zone, and let sc.gfp_mask handle it all.  That worries you?

Hugh
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