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References: <20211123190916.1738458-1-shakeelb@google.com> <20211124201238.3xzpy2b5zcv7j23s@box.shutemov.name>
In-Reply-To: <20211124201238.3xzpy2b5zcv7j23s@box.shutemov.name>
From:   Shakeel Butt <shakeelb@google.com>
Date:   Wed, 24 Nov 2021 12:44:02 -0800
Message-ID: <CALvZod6zUsCajhYcQOod+Nf0Y34x_sS1nnc7zAXUwZX0w3jzTw@mail.gmail.com>
Subject: Re: [PATCH v2] mm: thp: update split_queue_len correctly
To:     "Kirill A. Shutemov" <kirill@shutemov.name>
Cc:     David Hildenbrand <david@redhat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Yang Shi <shy828301@gmail.com>, Zi Yan <ziy@nvidia.com>,
        Matthew Wilcox <willy@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
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On Wed, Nov 24, 2021 at 12:12 PM Kirill A. Shutemov
<kirill@shutemov.name> wrote:
>
> On Tue, Nov 23, 2021 at 11:09:16AM -0800, Shakeel Butt wrote:
> > The deferred THPs are split on memory pressure through shrinker
> > callback and splitting of THP during reclaim can fail for several
> > reasons like unable to lock the THP, under writeback or unexpected
> > number of pins on the THP. Such pages are put back on the deferred split
> > list for consideration later. However kernel does not update the
> > deferred queue size on putting back the pages whose split was failed.
> > This patch fixes that.
>
> Hm. No. split_huge_page_to_list() updates the queue size on split success.
>

Right. This is really convoluted. split_huge_page_to_list() is just
assuming that if the given page is on a deferred list then it must be
on the list returned by get_deferred_split_queue(page). The
interaction of move_charge and deferred split seems broken.

Andrew, can you please drop this patch?