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 10:11:00 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     Muchun Song <songmuchun@...edance.com>
cc:     akpm@...ux-foundation.org, zi.yan@...rutgers.edu,
        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 Mon, 24 Jan 2022, 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.
> 

The mention of being backportable suggests that we should backport this, 
likely to 4.14+.  So should it be marked as stable?

That aside, should there be a follow-up patch that converts to using 
flush_dcache_folio()?

> 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
> 
> 
>