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Fri, 19 Dec 2025 09:42:21 +0800 Message-ID: Date: Fri, 19 Dec 2025 09:42:20 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: Consider non-anon swap cache folios in folio_expected_ref_count() To: Wei Yang , "David Hildenbrand (Red Hat)" Cc: Zi Yan , Bijan Tabatabai , linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, shivankg@amd.com, Hugh Dickins , Chris Li , Kairui Song References: <20251216200727.2360228-1-bijan311@gmail.com> <6b4cadb2-6246-48cc-9c76-64ba0a23198b@kernel.org> <0C218C18-916B-4BB0-8B37-AC82503E4AD9@nvidia.com> <20251219002134.uqgtnr43zz7vvvtd@master> From: Baolin Wang In-Reply-To: <20251219002134.uqgtnr43zz7vvvtd@master> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam02 X-Stat-Signature: zpkdjwjn5f8acxtbp1y9dfrazoxe75ww X-Rspam-User: X-Rspamd-Queue-Id: A303D140005 X-HE-Tag: 1766108545-303593 X-HE-Meta: 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 bGwG4+Se tj3pmQXI5Eb1pMUBh9kMHLBxuI6IqfGVUO9/xZG5A688hBJ48Ux5wKWnla2GQbQc7BVInU4j1dkOIxLllbXbtDjFiFhm7qSjuubN05aqOUkNKIgsn+zMiiPnZXxggIdQKM39JgrDEOexZ1jbEWYUvjVE/obsbbQPCIt0edFLZj54cpyJ24ZBJmGMftVHEfzvMckuqDCHdv3Mt+lC7G6WyMSdyqVgtHWAlQqxn9eZpT4cQfdPK5dNuUoiMBPiDuiGL0WtRgT6FCbcPLvyzyWfvzJbfHcZlTuyc2/wuPk5Bo7dYSpf1wwBO9hl9oP+zB5Xw3ceFR3KJqAFS5WfBOWUdZKRAVBzeiqgHC99HgZC8PdwS/928CbE4YK2FI+bBoU1WoY+r+tyZuhwpQlapVN/DOUeLK70pR6j6To6udzBEQMs5rmzbm6G8RkthqQ== 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 2025/12/19 08:21, Wei Yang wrote: > On Wed, Dec 17, 2025 at 02:04:16AM +0100, David Hildenbrand (Red Hat) wrote: >>>>> >>>>> I am not very familiar with the memory hot-(un)plug or swapping code, so >>>>> I am not 100% certain if this patch actually solves the root of the >>>>> problem. I believe the issue is from shmem folios, in which case I believe >>>>> this patch is correct. However, I couldn't think of an easy way to confirm >>>>> that the affected folios were from shmem. I guess it could be possible that >>>>> the root cause could be from some bug where some anonymous pages do not >>>>> return true to folio_test_anon(). I don't think that's the case, but >>>>> figured the MM maintainers would have a better idea of what's going on. >>> >>> I am not sure about if shmem in swapcache causes the issue, since >>> the above setup does not involve shmem. +Baolin and Hugh for some insight. >> >> We might just push out another unrelated shmem page to swap as we create >> memory pressure in the system I think. >> > > One trivial question: currently we only put anon/shmem folio in swapcache, > right? AFAICT, Yes (note a special case for anonymous folios: lazyfree anonymous folios will be directly freed instead of being swapped out).