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From: Michal Hocko <mhocko@kernel.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Vlastimil Babka <vbabka@suse.cz>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Mel Gorman <mgorman@techsingularity.net>,
	David Rientjes <rientjes@google.com>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	stable@vger.kernel.org
Subject: Re: [PATCH] mm, page_alloc: do not break __GFP_THISNODE by zonelist reset
Date: Mon, 28 May 2018 09:21:43 +0200
Message-ID: <20180528072143.GB1517@dhcp22.suse.cz> (raw)
In-Reply-To: <20180525124300.964a1a15d953e8972625bb0f@linux-foundation.org>

On Fri 25-05-18 12:43:00, Andrew Morton wrote:
> On Fri, 25 May 2018 15:08:53 +0200 Vlastimil Babka <vbabka@suse.cz> wrote:
> 
> > we might consider this for 4.17 although I don't know if there's anything
> > currently broken. Stable backports should be more important, but will have to
> > be reviewed carefully, as the code went through many changes.
> > BTW I think that also the ac->preferred_zoneref reset is currently useless if
> > we don't also reset ac->nodemask from a mempolicy to NULL first (which we
> > probably should for the OOM victims etc?), but I would leave that for a
> > separate patch.
> 
> Confused.  If nothing is currently broken then why is a backport
> needed?  Presumably because we expect breakage in the future?  Can you
> expand on this?

__GFP_THISNODE is documented to _use_ the given node. Allocating from a
different one is a bug. Maybe the current code can cope with that or at
least doesn't blow up in an obvious way but the bug is still there.

I am still not sure what to do about the zonelist reset. It still seems
like an echo from the past but using numa_node_id for __GFP_THISNODE is
a clear bug because our task could have been migrated to a cpu on a
different than requested node.

Acked-by: Michal Hocko <mhocko@suse.com>

-- 
Michal Hocko
SUSE Labs

  parent reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-25 13:08 Vlastimil Babka
2018-05-25 19:43 ` Andrew Morton
2018-05-25 20:48   ` Vlastimil Babka
2018-05-28  9:55     ` Vlastimil Babka
2018-05-28  7:21   ` Michal Hocko [this message]
2018-05-28 10:00     ` Vlastimil Babka
2018-05-28  8:49 ` Mel Gorman

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