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

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Message-ID: <0d7a4405-9a2e-4bd1-ba89-a31486155233@redhat.com>
Date: Tue, 4 Jun 2024 15:47:09 +0200
From: David Hildenbrand <david@...hat.com>
To: yangge1116@....com, akpm@...ux-foundation.org
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 baolin.wang@...ux.alibaba.com, liuzixing@...on.cn
Subject: Re: [PATCH] mm/gup: don't check page lru flag before draining it

On 04.06.24 12:48, 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 referenced 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
> referenced by pagevec.

What you are saying is that we might have a page on which 
folio_test_lru() succeeds, that was added to one of the cpu_fbatches, 
correct?

Can you describe under which circumstances that happens?

-- 
Cheers,

David / dhildenb