linux-kernel - Re: [PATCH] mm/thp: decrease nr_thps in file's mapping on THP split

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Date:   Tue, 12 Oct 2021 13:43:35 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        김성훈 <sfoon.kim@...sung.com>,
        Song Liu <songliubraving@...com>,
        Rik van Riel <riel@...riel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Hillf Danton <hdanton@...a.com>,
        Hugh Dickins <hughd@...gle.com>,
        William Kucharski <william.kucharski@...cle.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>
Subject: Re: [PATCH] mm/thp: decrease nr_thps in file's mapping on THP split

On Tue, Oct 12, 2021 at 02:02:37PM +0200, Marek Szyprowski wrote:
> Decrease nr_thps counter in file's mapping to ensure that the page cache
> won't be dropped excessively on file write access if page has been
> already splitted.
> 
> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
> Fixes: 09d91cda0e82 ("mm,thp: avoid writes to file with THP in pagecache")
> Fixes: 06d3eff62d9d ("mm/thp: fix node page state in split_huge_page_to_list()")
> ---
> I've analyzed the code a few times but either I missed something or the
> nr_thps counter is not decremented during the THP split on non-shmem file
> pages.

This looks OK to me, but have you tested it?  If so, what workload did
you use?  The way you wrote this changelog makes it sound like you only
read the code and there have been rather too many bugs introduced recently
that way :-(