linux-kernel - Re: [PATCH v1 1/3] mm: Allow deferred splitting of arbitrary large anon folios

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Date:   Mon, 17 Jul 2023 17:42:01 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Ryan Roberts <ryan.roberts@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Yin Fengwei <fengwei.yin@...el.com>,
        Yu Zhao <yuzhao@...gle.com>, Yang Shi <shy828301@...il.com>,
        "Huang, Ying" <ying.huang@...el.com>, Zi Yan <ziy@...dia.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v1 1/3] mm: Allow deferred splitting of arbitrary large
 anon folios

On 17.07.23 16:31, Ryan Roberts wrote:
> In preparation for the introduction of large folios for anonymous
> memory, we would like to be able to split them when they have unmapped
> subpages, in order to free those unused pages under memory pressure. So
> remove the artificial requirement that the large folio needed to be at
> least PMD-sized.
> 
> Signed-off-by: Ryan Roberts <ryan.roberts@....com>
> Reviewed-by: Yu Zhao <yuzhao@...gle.com>
> Reviewed-by: Yin Fengwei <fengwei.yin@...el.com>
> ---
>   mm/rmap.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 0c0d8857dfce..2baf57d65c23 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1430,7 +1430,7 @@ void page_remove_rmap(struct page *page, struct vm_area_struct *vma,
>   		 * page of the folio is unmapped and at least one page
>   		 * is still mapped.
>   		 */
> -		if (folio_test_pmd_mappable(folio) && folio_test_anon(folio))
> +		if (folio_test_large(folio) && folio_test_anon(folio))
>   			if (!compound || nr < nr_pmdmapped)
>   				deferred_split_folio(folio);

!compound will always be true I guess, so nr_pmdmapped == 0 (which will 
always be the case) will be ignored.

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb