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Fri, 12 Sep 2025 10:18:00 -0700 (PDT) MIME-Version: 1.0 References: <20250910160833.3464-1-ryncsn@gmail.com> <20250910160833.3464-5-ryncsn@gmail.com> In-Reply-To: <20250910160833.3464-5-ryncsn@gmail.com> From: Nhat Pham Date: Fri, 12 Sep 2025 10:17:48 -0700 X-Gm-Features: Ac12FXxE3rEVvClbzQKrM7cmqGE6Iqd2PgJQy7xb8lu-dQtSlZcYF-4hgXQEdFk Message-ID: Subject: Re: [PATCH v3 04/15] mm, swap: check page poison flag after locking it To: Kairui Song Cc: linux-mm@kvack.org, Andrew Morton , Matthew Wilcox , Hugh Dickins , Chris Li , Barry Song , Baoquan He , Kemeng Shi , Baolin Wang , Ying Huang , Johannes Weiner , David Hildenbrand , Yosry Ahmed , Lorenzo Stoakes , Zi Yan , linux-kernel@vger.kernel.org, Kairui Song Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: C1699100002 X-Stat-Signature: d8q6h6xqxokbkywcaa1yqcbhcqu97d6j X-Rspam-User: X-HE-Tag: 1757697481-397308 X-HE-Meta: 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 Gq5LqTbf VvjxXdRq5mtC8/byyDGxZSn1HLuuhFrdXzQu0/BrdSvz+ki4IWumY8PB3OGI1pq7eEnsTBkFOk0gmOuwcZ/c28G2CNrFT2YSjDiv8oGgP5rtxYxasMaKHZ8XtFYnkov+bGB0P896S4ICf1egQYRlvcJskOp0HbPrpdiQyZOrsQmTy9g/mtLnEoIdTcj2DIo/FiktZgULqUP+huDtOowxVYIHalucRltm2hFUpiFs/JAw9jDt35CC2WwcVwDscZibtqcpNOzAgMEsyJRfRtil8dwaOrOw3fvpjs2h0Zspk3J4Cbo9R0ndR6QjtA+MhnTOhUpDaxsj9gxeQeVgbmAjhPm0n75R/lJRBZmfyu3yBEDh2jZlIo/nTDkte7lAbuYyRespQ3SQuHM6P02Fu6R8J3gH4TNKIvKtCVJ9bVDXQUFAhOkk= 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 Wed, Sep 10, 2025 at 9:09=E2=80=AFAM Kairui Song wrot= e: > > From: Kairui Song > > Instead of checking the poison flag only in the fast swap cache lookup > path, always check the poison flags after locking a swap cache folio. > > There are two reasons to do so. > > The folio is unstable and could be removed from the swap cache anytime, > so it's totally possible that the folio is no longer the backing folio > of a swap entry, and could be an irrelevant poisoned folio. We might > mistakenly kill a faulting process. > > And it's totally possible or even common for the slow swap in path > (swapin_readahead) to bring in a cached folio. The cache folio could be > poisoned, too. Only checking the poison flag in the fast path will miss > such folios. > > The race window is tiny, so it's very unlikely to happen, though. > While at it, also add a unlikely prefix. > > Signed-off-by: Kairui Song > Acked-by: Chris Li Acked-by: Nhat Pham