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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1uyG6K-00000006bmk-1w1p; Mon, 15 Sep 2025 20:47:04 +0000 Date: Mon, 15 Sep 2025 21:47:04 +0100 From: Matthew Wilcox To: Baolin Wang Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, david@redhat.com, mhocko@kernel.org, zhengqi.arch@bytedance.com, shakeel.butt@linux.dev, lorenzo.stoakes@oracle.com, hughd@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] mm: vmscan: remove folio_test_private() check in pageout() Message-ID: References: <11629632-c652-460e-b617-3ec0c27969f5@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <11629632-c652-460e-b617-3ec0c27969f5@linux.alibaba.com> X-Rspamd-Queue-Id: B5ADF1C0007 X-Stat-Signature: azq7owg9d98ijbpur39ipj8g47mwo96i X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1757969236-530360 X-HE-Meta: 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, Sep 13, 2025 at 11:04:48AM +0800, Baolin Wang wrote: > On 2025/9/12 23:21, Matthew Wilcox wrote: > > On Fri, Sep 12, 2025 at 11:45:07AM +0800, Baolin Wang wrote: > > > @@ -697,22 +697,8 @@ static pageout_t pageout(struct folio *folio, struct address_space *mapping, > > > * swap_backing_dev_info is bust: it doesn't reflect the > > > * congestion state of the swapdevs. Easy to fix, if needed. > > > */ > > > - if (!is_page_cache_freeable(folio)) > > > + if (!is_page_cache_freeable(folio) || !mapping) > > > return PAGE_KEEP; > > > > I feel like we need to keep the comment (assuming it's still true ... > > which it probably is, although there's nobody who would think to update > > this comment if it became no longer true). I would certainly wonder why > > we can have this !mapping test. > > I think the !mapping check is still needed here because the tmpfs/shmem > folios truncation might race with folio reclamation, see shmem_undo_range(). I agree that we still need the !mapping check. But it needs this comment that you're deleting, because it's not obvious why we'd have a dirty folio with a NULL mapping on the LRU list. > > > - /* > > > - * Some data journaling orphaned folios can have > > > - * folio->mapping == NULL while being dirty with clean buffers. > > > - */