linux-kernel - Re: [PATCH] mm: page-writeback: simplify memcg handling in test_clear_page

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Message-ID: <CALvZod7Tf+KBhT=3WCQ_uWa7_mZad6-L8wQJghxPRL_tVyQ8Cw@mail.gmail.com>
Date:   Wed, 10 Feb 2021 05:46:51 -0800
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        Michal Hocko <mhocko@...e.com>, Roman Gushchin <guro@...com>,
        Linux MM <linux-mm@...ck.org>,
        Cgroups <cgroups@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH] mm: page-writeback: simplify memcg handling in test_clear_page_writeback()

On Tue, Feb 9, 2021 at 1:45 PM Johannes Weiner <hannes@...xchg.org> wrote:
>
> Page writeback doesn't hold a page reference, which allows truncate to
> free a page the second PageWriteback is cleared. This used to require
> special attention in test_clear_page_writeback(), where we had to be
> careful not to rely on the unstable page->memcg binding and look up
> all the necessary information before clearing the writeback flag.
>
> Since commit 073861ed77b6 ("mm: fix VM_BUG_ON(PageTail) and
> BUG_ON(PageWriteback)") test_clear_page_writeback() is called with an
> explicit reference on the page, and this dance is no longer needed.
>
> Use unlock_page_memcg() and dec_lruvec_page_stat() directly.
>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

Reviewed-by: Shakeel Butt <shakeelb@...gle.com>