linux-kernel - Re: [PATCH v5 4/9] mm/migrate: clear __GFP_RECLAIM to make the migration callback consistent with regular THP allocations

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Date:   Tue, 14 Jul 2020 09:44:59 +0900
From:   Joonsoo Kim <js1304@...il.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel-team@....com,
        Christoph Hellwig <hch@...radead.org>,
        Roman Gushchin <guro@...com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH v5 4/9] mm/migrate: clear __GFP_RECLAIM to make the
 migration callback consistent with regular THP allocations

On Mon, Jul 13, 2020 at 09:52:20AM +0200, Vlastimil Babka wrote:
> On 7/13/20 8:41 AM, js1304@...il.com wrote:
> > From: Joonsoo Kim <iamjoonsoo.kim@....com>
> > 
> > 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.
> > 
> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> 
> Acked-by: Vlastimil Babka <vbabka@...e.cz>
> 
> Thanks!
> 
> Typo below (I assume Andrew will fix it)
> 
> > ---
> >  mm/migrate.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/mm/migrate.c b/mm/migrate.c
> > index 3b3d918..1cfc965 100644
> > --- a/mm/migrate.c
> > +++ b/mm/migrate.c
> > @@ -1547,6 +1547,11 @@ struct page *new_page_nodemask(struct page *page,
> >  	}
> >  
> >  	if (PageTransHuge(page)) {
> > +		/*
> > +		 * clear __GFP_RECALIM to make the migration callback
> 
>                          __GFP_RECLAIM
> 

Okay. Here goes a fixed version.

Thanks!


---------------------->8-----------------------------
>From 6273f02fd8b8ef066c10c4a8ba54ea9efe6e70cd Mon Sep 17 00:00:00 2001
From: Joonsoo Kim <iamjoonsoo.kim@....com>
Date: Mon, 6 Jul 2020 14:34:04 +0900
Subject: [PATCH v5 4/9] mm/migrate: clear __GFP_RECLAIM to make the migration
 callback consistent with regular THP allocations

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.

Acked-by: Michal Hocko <mhocko@...e.com>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
---
 mm/migrate.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/migrate.c b/mm/migrate.c
index 3b3d918..faabb2e 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1547,6 +1547,11 @@ struct page *new_page_nodemask(struct page *page,
 	}
 
 	if (PageTransHuge(page)) {
+		/*
+		 * clear __GFP_RECLAIM to make the migration callback
+		 * consistent with regular THP allocations.
+		 */
+		gfp_mask &= ~__GFP_RECLAIM;
 		gfp_mask |= GFP_TRANSHUGE;
 		order = HPAGE_PMD_ORDER;
 	}
-- 
2.7.4