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Subject: Re: [PATCH v5 4/9] mm/migrate: clear __GFP_RECLAIM to make the
 migration callback consistent with regular THP allocations
To:     js1304@gmail.com, Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        kernel-team@lge.com, Christoph Hellwig <hch@infradead.org>,
        Roman Gushchin <guro@fb.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
        Michal Hocko <mhocko@suse.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>
References: <1594622517-20681-1-git-send-email-iamjoonsoo.kim@lge.com>
 <1594622517-20681-5-git-send-email-iamjoonsoo.kim@lge.com>
From:   Vlastimil Babka <vbabka@suse.cz>
Message-ID: <367ca602-1112-f87f-7d2a-b0a75cce7269@suse.cz>
Date:   Mon, 13 Jul 2020 09:52:20 +0200
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On 7/13/20 8:41 AM, js1304@gmail.com wrote:
> From: Joonsoo Kim <iamjoonsoo.kim@lge.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@lge.com>

Acked-by: Vlastimil Babka <vbabka@suse.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

> +		 * consistent with regular THP allocations.
> +		 */
> +		gfp_mask &= ~__GFP_RECLAIM;
>  		gfp_mask |= GFP_TRANSHUGE;
>  		order = HPAGE_PMD_ORDER;
>  	}
>