linux-kernel - Re: ppc: RECLAIM

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Message-ID: <20140219083327.GC14783@dhcp22.suse.cz>
Date:	Wed, 19 Feb 2014 09:33:27 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	linuxppc-dev@...ts.ozlabs.org, Anton Blanchard <anton@...ba.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: ppc: RECLAIM_DISTANCE 10?

On Tue 18-02-14 17:43:38, David Rientjes wrote:
> On Tue, 18 Feb 2014, Nishanth Aravamudan wrote:
> 
> > How about the following?
> > 
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 5de4337..1a0eced 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -1854,7 +1854,8 @@ static void __paginginit init_zone_allows_reclaim(int nid)
> >         int i;
> >  
> >         for_each_online_node(i)
> > -               if (node_distance(nid, i) <= RECLAIM_DISTANCE)
> > +               if (node_distance(nid, i) <= RECLAIM_DISTANCE ||
> > +                                       !NODE_DATA(i)->node_present_pages)
> >                         node_set(i, NODE_DATA(nid)->reclaim_nodes);
> >                 else
> >                         zone_reclaim_mode = 1;
> 
>  [ I changed the above from NODE_DATA(nid) -> NODE_DATA(i) as you caught 
>    so we're looking at the right code. ]
> 
> That can't be right, it would allow reclaiming from a memoryless node.  I 
> think what you want is
> 
> 	for_each_online_node(i) {
> 		if (!node_present_pages(i))
> 			continue;
> 		if (node_distance(nid, i) <= RECLAIM_DISTANCE) {
> 			node_set(i, NODE_DATA(nid)->reclaim_nodes);
> 			continue;
> 		}
> 		/* Always try to reclaim locally */
> 		zone_reclaim_mode = 1;
> 	}
> 
> but we really should be able to do for_each_node_state(i, N_MEMORY) here 
> and memoryless nodes should already be excluded from that mask.

Agreed! Actually the code I am currently interested in is based on 3.0
kernel where zone_reclaim_mode is set in build_zonelists which relies on
find_next_best_node which iterates only N_HIGH_MEMORY nodes which should
have non 0 present pages.
[...]
-- 
Michal Hocko
SUSE Labs
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