linux-kernel - Re: [PATCH 6/6] mm, migration: do not trigger OOM killer when migrating memory

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Date:   Mon, 26 Jun 2017 07:28:27 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...e.de>, NeilBrown <neilb@...e.com>,
        LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [PATCH 6/6] mm, migration: do not trigger OOM killer when
 migrating memory

On Fri 23-06-17 13:43:05, Andrew Morton wrote:
> On Fri, 23 Jun 2017 10:53:45 +0200 Michal Hocko <mhocko@...nel.org> wrote:
> 
> > From: Michal Hocko <mhocko@...e.com>
> > 
> > Page migration (for memory hotplug, soft_offline_page or mbind) needs
> > to allocate a new memory. This can trigger an oom killer if the target
> > memory is depleated. Although quite unlikely, still possible, especially
> > for the memory hotplug (offlining of memoery). Up to now we didn't
> > really have reasonable means to back off. __GFP_NORETRY can fail just
> > too easily and __GFP_THISNODE sticks to a single node and that is not
> > suitable for all callers.
> > 
> > But now that we have __GFP_RETRY_MAYFAIL we should use it.  It is
> > preferable to fail the migration than disrupt the system by killing some
> > processes.
> 
> I'm not sure which tree this is against...

next-20170623

> 
> > --- a/mm/memory-failure.c
> > +++ b/mm/memory-failure.c
> > @@ -1492,7 +1492,8 @@ static struct page *new_page(struct page *p, unsigned long private, int **x)
> >  
> >  		return alloc_huge_page_node(hstate, nid);
> >  	} else {
> > -		return __alloc_pages_node(nid, GFP_HIGHUSER_MOVABLE, 0);
> > +		return __alloc_pages_node(nid,
> > +				GFP_HIGHUSER_MOVABLE | __GFP_RETRY_MAYFAIL, 0);
> >  	}
> >  }
> 
> new_page() is now
> 
> static struct page *new_page(struct page *p, unsigned long private, int **x)
> {
> 	int nid = page_to_nid(p);
> 
> 	return new_page_nodemask(p, nid, &node_states[N_MEMORY]);
> }
> 
> and new_page_nodemask() uses __GFP_RETRY_MAYFAIL so I simply dropped
> the above hunk.

Ohh, right. This is
http://lkml.kernel.org/r/20170622193034.28972-4-mhocko@kernel.org. I've
just didn't realize it was not in mmotm yet. So yes the hunk can be
dropped, new_page_nodemask does what we need.
 
Sorry about that
-- 
Michal Hocko
SUSE Labs