linux-kernel - Re: [PATCH v2 2/8] mm: migrate: remove THP mapcount check in numamigrate_isolate

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Message-ID: <87ttsrbytl.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date:   Tue, 22 Aug 2023 10:22:46 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, <willy@...radead.org>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <david@...hat.com>, Zi Yan <ziy@...dia.com>,
        Mike Kravetz <mike.kravetz@...cle.com>, <hughd@...gle.com>
Subject: Re: [PATCH v2 2/8] mm: migrate: remove THP mapcount check in
 numamigrate_isolate_page()

Kefeng Wang <wangkefeng.wang@...wei.com> writes:

> The check of THP mapped by multiple processes was introduced by commit
> 04fa5d6a6547 ("mm: migrate: check page_count of THP before migrating")
> and refactor by commit 340ef3902cf2 ("mm: numa: cleanup flow of transhuge
> page migration"), which is out of date, since migrate_misplaced_page()
> is now using the standard migrate_pages() for small pages and THPs, the
> reference count checking is in folio_migrate_mapping(), so let's remove
> the special check for THP.
>
> Suggested-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>

Reviewed-by: "Huang, Ying" <ying.huang@...el.com>

> ---
>  mm/migrate.c | 4 ----
>  1 file changed, 4 deletions(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 646d8ee7f102..f2d86dfd8423 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2483,10 +2483,6 @@ static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
>  	int nr_pages = thp_nr_pages(page);
>  	int order = compound_order(page);
>  
> -	/* Do not migrate THP mapped by multiple processes */
> -	if (PageTransHuge(page) && total_mapcount(page) > 1)
> -		return 0;
> -
>  	/* Avoid migrating to a node that is nearly full */
>  	if (!migrate_balanced_pgdat(pgdat, nr_pages)) {
>  		int z;