linux-kernel - Re: [PATCH v2 1/9] mm/vmscan: add a comment about MADV_FREE pages check in folio_check_dirty

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Message-ID: <4b7923585e07b0238545ebb997af92eeadcdaf78.camel@intel.com>
Date:   Mon, 11 Apr 2022 19:50:42 +0800
From:   "ying.huang@...el.com" <ying.huang@...el.com>
To:     Miaohe Lin <linmiaohe@...wei.com>, akpm@...ux-foundation.org
Cc:     songmuchun@...edance.com, hch@...radead.org, willy@...radead.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/9] mm/vmscan: add a comment about MADV_FREE pages
 check in folio_check_dirty_writeback

On Sat, 2022-04-09 at 17:34 +0800, Miaohe Lin wrote:
> The MADV_FREE pages check in folio_check_dirty_writeback is a bit hard to
> follow. Add a comment to make the code clear.
> 
> Suggested-by: Huang, Ying <ying.huang@...el.com>
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  mm/vmscan.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index c77d5052f230..4a76be47bed1 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1436,6 +1436,9 @@ static void folio_check_dirty_writeback(struct folio
> *folio,
>         /*
>          * Anonymous pages are not handled by flushers and must be written
>          * from reclaim context. Do not stall reclaim based on them
> +        * MADV_FREE anonymous pages are put into inactive file list too.
> +        * They could be mistakenly treated as file lru. So further anon
> +        * test is needed.
>          */

How about something as follows,

	/*
         * Anonymous pages (including MADV_FREE ones) are not handled
by	 * flushers and must be written from reclaim context. Do not stall
	 * reclaim based on them
	 */.

Best Regards,
Huang, Ying

>         if (!folio_is_file_lru(folio) ||
>             (folio_test_anon(folio) && !folio_test_swapbacked(folio))) {