Re: [PATCH 6.6 06/60] mm: migrate: remove THP mapcount check in numamigrate_isolate_page()

[Hugh Dickins <hughd@google.com>]

On Wed, 13 Mar 2024, Sasha Levin wrote:

> From: Kefeng Wang <wangkefeng.wang@huawei.com>
> 
> [ Upstream commit 728be28fae8c838d52c91dce4867133798146357 ]
> 
> 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 migration"), which is out of date, since migrate_misplaced_page() is now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.
> 
> Link: https://lkml.kernel.org/r/20230913095131.2426871-3-wangkefeng.wang@huawei.com
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Mike Kravetz <mike.kravetz@oracle.com>
> Cc: Zi Yan <ziy@nvidia.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Stable-dep-of: 2774f256e7c0 ("mm/vmscan: fix a bug calling wakeup_kswapd() with a wrong zone index")

No it is not: that one is appropriate to include, this one is not.

Hugh

> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
>  mm/migrate.c | 4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 6f8ad6b64c9bc..c9fabb960996f 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2506,10 +2506,6 @@ 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;
> -- 
> 2.43.0
> 
>