linux-kernel - Re: [RFC] mm/thp: Update mm's MM_ANONPAGES stat in set_huge_zero

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Message-ID: <1B37E0D8-2F69-45A3-9384-DC5BCE9F67A8@nvidia.com>
Date:   Thu, 13 May 2021 10:12:00 -0400
From:   Zi Yan <ziy@...dia.com>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC] mm/thp: Update mm's MM_ANONPAGES stat in set_huge_zero_page()

On 13 May 2021, at 3:20, Anshuman Khandual wrote:

> Although the zero huge page is being shared across various processes, each
> mapping needs to update its mm's MM_ANONPAGES stat by HPAGE_PMD_NR in order
> to be consistent. This just updates the stats in set_huge_zero_page() after
> the mapping gets created.

In addition, MM_ANONPAGES stats should be decreased at zap_huge_pmd() and
__split_huge_pmd_locked() when the zero huge page mapping is removed from
a process, right?

>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Zi Yan <ziy@...dia.com>
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
> Should it update MM_SHMEM_PAGES instead ? Applies on latest mainline.

zero huge page is added via do_huge_pmd_anonymous_page(), I think MM_ANONPAGES
is appropriate.

>
>  mm/huge_memory.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 63ed6b25deaa..262703304807 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -706,6 +706,7 @@ static void set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
>  	if (pgtable)
>  		pgtable_trans_huge_deposit(mm, pmd, pgtable);
>  	set_pmd_at(mm, haddr, pmd, entry);
> +	add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
>  	mm_inc_nr_ptes(mm);
>  }
>
> -- 
> 2.20.1


—
Best Regards,
Yan Zi

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