linux-kernel - Re: [PATCH] mm/gup: don't check page lru flag before draining it

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Date: Tue, 4 Jun 2024 16:56:08 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: yangge1116@....com, akpm@...ux-foundation.org
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, liuzixing@...on.cn
Subject: Re: [PATCH] mm/gup: don't check page lru flag before draining it



On 2024/6/4 16:09, yangge1116@....com wrote:
> From: yangge <yangge1116@....com>
> 
> If a page is added in pagevec, its ref count increases one, remove
> the page from pagevec decreases one. Page migration requires the
> page is not referrened by others except page mapping. Before
> migrating a page, we should try to drain the page from pagevec in
> case the page is in it, however, folio_test_lru() is not sufficient
> to tell whether the page is in pagevec or not, if the page is in
> pagevec, the migration will fail.
> 
> Remove the condition and drain lru once to ensure the page is not
> referrenced by pagevec.

This looks sane to me and seems a simple way to fix.

> Signed-off-by: yangge <yangge1116@....com>
> ---
>   mm/gup.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index ca0f5ce..890dcbc 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2411,7 +2411,7 @@ static unsigned long collect_longterm_unpinnable_pages(
>   			continue;
>   		}
>   
> -		if (!folio_test_lru(folio) && drain_allow) {
> +		if (drain_allow) {
>   			lru_add_drain_all();
>   			drain_allow = false;
>   		}

You should rebase your code on the latest mm-unstable branch, as 
collect_longterm_unpinnable_pages() in the upstream has been replaced 
with collect_longterm_unpinnable_folios().