linux-kernel - Re: [PATCH 2/2] mm, thp: consolidate THP gfp handling into alloc_hugepage_direct

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Date:   Thu, 25 Oct 2018 06:56:37 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Michal Hocko <mhocko@...nel.org>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Mel Gorman <mgorman@...e.de>,
        David Rientjes <rientjes@...gle.com>,
        Andrea Argangeli <andrea@...nel.org>,
        Zi Yan <zi.yan@...rutgers.edu>,
        Stefan Priebe - Profihost AG <s.priebe@...fihost.ag>,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] mm, thp: consolidate THP gfp handling into
 alloc_hugepage_direct_gfpmask

On 10/25/18 1:17 AM, Andrew Morton wrote:
> On Mon, 22 Oct 2018 15:27:54 +0200 Vlastimil Babka <vbabka@...e.cz> wrote:
> 
>>> : Moreover the oriinal code allowed to trigger
>>> : 	WARN_ON_ONCE(policy->mode == MPOL_BIND && (gfp & __GFP_THISNODE));
>>> : in policy_node if the requested node (e.g. cpu local one) was outside of
>>> : the mbind nodemask. This is not possible now. We haven't heard about any
>>> : such warning yet so it is unlikely that it happens but still a signal of
>>> : a wrong code layering.
>>
>> Ah, as I said in the other mail, I think it's inaccurate, the warning
>> was not possible to hit.
>>
>> There's also a slight difference wrt MPOL_BIND. The previous code would
>> avoid using __GFP_THISNODE if the local node was outside of
>> policy_nodemask(). After your patch __GFP_THISNODE is avoided for all
>> MPOL_BIND policies. So there's a difference that if local node is
>> actually allowed by the bind policy's nodemask, previously
>> __GFP_THISNODE would be added, but now it won't be. I don't think it
>> matters that much though, but maybe the changelog could say that
>> (instead of the inaccurate note about warning). Note the other policy
>> where nodemask is relevant is MPOL_INTERLEAVE, and that's unchanged by
>> this patch.
> 
> So the above could go into the changelog, yes?

Yeah.

>> When that's addressed, you can add
> 
> What is it that you'd like to see addressed?  Purely changelog updates?

Right.

>> Acked-by: Vlastimil Babka <vbabka@...e.cz>
> 
> Thanks.
>