linux-kernel - Re: [PATCH v4 05/11] mm/migrate: clear __GFP_RECLAIM for THP allocation for migration

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Date:   Thu, 9 Jul 2020 12:26:30 +0900
From:   Joonsoo Kim <js1304@...il.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>, kernel-team@....com,
        Vlastimil Babka <vbabka@...e.cz>,
        Christoph Hellwig <hch@...radead.org>,
        Roman Gushchin <guro@...com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Subject: Re: [PATCH v4 05/11] mm/migrate: clear __GFP_RECLAIM for THP
 allocation for migration

2020년 7월 8일 (수) 오후 4:48, Michal Hocko <mhocko@...nel.org>님이 작성:
>
> On Wed 08-07-20 16:19:17, Joonsoo Kim wrote:
> > On Tue, Jul 07, 2020 at 01:40:19PM +0200, Michal Hocko wrote:
> [...]
> > Subject: [PATCH] mm/migrate: clear __GFP_RECLAIM for THP allocation for
> >  migration
> >
> > In migration target allocation functions, THP allocations uses different
> > gfp_mask, especially, in regard to the reclaim gfp_mask. There is no
> > reason to use different reclaim gfp_mask for each cases and it is
> > an obstacle to make a common function in order to clean-up migration
> > target allocation functions. This patch fixes this situation by using
> > common reclaim gfp_mask for THP allocation.
>
> I would find the following more understandable, feel free to reuse parts
> that you like:
> "
> new_page_nodemask is a migration callback and it tries to use a common
> gfp flags for the target page allocation whether it is a base page or a
> THP. The later only adds GFP_TRANSHUGE to the given mask. This results
> in the allocation being slightly more aggressive than necessary because
> the resulting gfp mask will contain also __GFP_RECLAIM_KSWAPD. THP
> allocations usually exclude this flag to reduce over eager background
> reclaim during a high THP allocation load which has been seen during
> large mmaps initialization. There is no indication that this is a
> problem for migration as well but theoretically the same might happen
> when migrating large mappings to a different node. Make the migration
> callback consistent with regular THP allocations.
> "

Looks good!
I will use this description.

Thanks.