linux-kernel - Re: [PATCH v2 2/2] mm: fix missing cache flush for all tail pages of THP

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Date:   Mon, 24 Jan 2022 11:07:33 -0500
From:   Zi Yan <ziy@...dia.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     akpm@...ux-foundation.org, kirill.shutemov@...ux.intel.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        duanxiongchun@...edance.com
Subject: Re: [PATCH v2 2/2] mm: fix missing cache flush for all tail pages of THP

On 24 Jan 2022, at 0:17, Muchun Song wrote:

> The D-cache maintenance inside move_to_new_page() only consider one page,
> there is still D-cache maintenance issue for tail pages of THP. Fix this
> by not using flush_dcache_folio() since it is not backportable.
>
> Fixes: 616b8371539a ("mm: thp: enable thp migration in generic path")
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> ---
> Changes in v2:
>  - Using a for loop instead of the folio variant for backportable.
>
>  mm/migrate.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index c9296d63878d..c418e8d92b9c 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -933,9 +933,12 @@ static int move_to_new_page(struct page *newpage, struct page *page,
>  		if (!PageMappingFlags(page))
>  			page->mapping = NULL;
>
> -		if (likely(!is_zone_device_page(newpage)))
> -			flush_dcache_page(newpage);
> +		if (likely(!is_zone_device_page(newpage))) {
> +			int i, nr = compound_nr(newpage);
>
> +			for (i = 0; i < nr; i++)
> +				flush_dcache_page(newpage + i);
> +		}
>  	}
>  out:
>  	return rc;
> -- 
> 2.11.0

LGTM. Thanks. Reviewed-by: Zi Yan <ziy@...dia.com>

--
Best Regards,
Yan, Zi

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