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

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Date:   Fri, 21 Jan 2022 09:59:21 -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
Subject: Re: [PATCH 2/2] mm: fix missing cache flush for all tail pages of THP

On 21 Jan 2022, at 3:13, 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 using flush_dcache_folio().
>
> Fixes: 616b8371539a ("mm: thp: enable thp migration in generic path")
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> ---
>  mm/migrate.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index c9296d63878d..daf2b3508670 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -934,8 +934,7 @@ static int move_to_new_page(struct page *newpage, struct page *page,
>  			page->mapping = NULL;
>
>  		if (likely(!is_zone_device_page(newpage)))
> -			flush_dcache_page(newpage);
> -
> +			flush_dcache_folio(page_folio(newpage));
>  	}
>  out:
>  	return rc;
> -- 
> 2.11.0

Yes, the entire THP should be flushed. But it is better
to use a for loop instead of the folio variant, so that the patch
can be ported easily to the stable trees. The for loop can be
converted later when the whole function is converted to use folio.

Thanks.

--
Best Regards,
Yan, Zi

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