linux-kernel - Re: [PATCH v2] mm: thp: update split_queue

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Message-ID: <CALvZod6zUsCajhYcQOod+Nf0Y34x_sS1nnc7zAXUwZX0w3jzTw@mail.gmail.com>
Date:   Wed, 24 Nov 2021 12:44:02 -0800
From:   Shakeel Butt <shakeelb@...gle.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     David Hildenbrand <david@...hat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Yang Shi <shy828301@...il.com>, Zi Yan <ziy@...dia.com>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm: thp: update split_queue_len correctly

On Wed, Nov 24, 2021 at 12:12 PM Kirill A. Shutemov
<kirill@...temov.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?