linux-kernel - Re: [PATCH] mm, page_alloc: do not break __GFP

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Date:   Mon, 28 May 2018 11:55:52 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Mel Gorman <mgorman@...hsingularity.net>,
        Michal Hocko <mhocko@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, stable@...r.kernel.org
Subject: Re: [PATCH] mm, page_alloc: do not break __GFP_THISNODE by zonelist
 reset

On 05/25/2018 10:48 PM, Vlastimil Babka wrote:
> On 05/25/2018 09:43 PM, Andrew Morton wrote:
>> On Fri, 25 May 2018 15:08:53 +0200 Vlastimil Babka <vbabka@...e.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?
> 
> I mean that SLAB is currently not affected, but in older kernels than
> 4.7 that don't yet have 511e3a058812 ("mm/slab: make cache_grow() handle
> the page allocated on arbitrary node") it is. That's at least 4.4 LTS.
> Older ones I'll have to check.

So I've checked the non-EOL LTS's at kernel.org and:

4.16, 4.14, 4.9 - same as mainline (__GFP_THISNODE broken, but SLAB is OK)
4.4, 4.1, 3.16 - SLAB potentially broken if it makes an
ALLOC_NO_WATERMARKS allocation (our 4.4 kernel has backports that extend
it to also !ALLOC_CPUSET so it's more likely).