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From:   Yu Zhao <yuzhao@google.com>
Date:   Wed, 2 Mar 2022 19:15:02 -0700
Message-ID: <CAOUHufbJnFNLmS+tKDhsi0jwyXupjNKbs2J_D_1Nqe3UhBOMFA@mail.gmail.com>
Subject: Re: [PATCH mmotm] mm: delete __ClearPageWaiters()
To:     Hugh Dickins <hughd@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Matthew Wilcox <willy@infradead.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        Yang Shi <shy828301@gmail.com>, Michal Hocko <mhocko@suse.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>
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On Wed, Mar 2, 2022 at 6:56 PM Hugh Dickins <hughd@google.com> wrote:
>
> The PG_waiters bit is not included in PAGE_FLAGS_CHECK_AT_FREE, and
> vmscan.c's free_unref_page_list() callers rely on that not to generate
> bad_page() alerts.  So __page_cache_release() and release_pages() (and
> the presumably copy-and-pasted put_zone_device_private_or_public_page())
> are redundant and misleading to make a special point of clearing it (as
> the "__" implies, it could only safely be used on the freeing path).
>
> Delete __ClearPageWaiters().  Remark on this in one of the "possible"
> comments in wake_up_page_bit(), and delete the superfluous comments.
>
> Signed-off-by: Hugh Dickins <hughd@google.com>
> ---
> We've used this since 2018, and I see Yu Zhao posted similar in 2020:
> https://lore.kernel.org/linux-mm/20200818184704.3625199-3-yuzhao@google.com/
> I couldn't join in at that time, but think its reception was over-cautious.

Indeed.

Tested-by: Yu Zhao <yuzhao@google.com>