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Mon, 28 Apr 2025 08:21:13 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id AcHsDXk6D2gafgAAD6G6ig (envelope-from ); Mon, 28 Apr 2025 08:21:13 +0000 Date: Mon, 28 Apr 2025 10:21:11 +0200 From: Oscar Salvador To: Kairui Song Cc: linux-mm@kvack.org, Andrew Morton , David Hildenbrand , linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/memory: fix mapcount / refcount sanity check for mTHP reuse Message-ID: References: <20250425074325.61833-1-ryncsn@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250425074325.61833-1-ryncsn@gmail.com> X-Rspamd-Action: no action X-Stat-Signature: pafp63g87bddc6z1isyaqq3hgibdzwj9 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 6F75E120012 X-Rspam-User: X-HE-Tag: 1745828475-242799 X-HE-Meta: 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 ukwQXsjA 8+sTHPcuyf6S5vW1tVX8JtWLhfp3Q5y/0JUkTbUmCZqhFMueaXN1SZSf6q1ZwLhPX22yZyVsA3jM9f5dk/GCLBOtlTXHBfnZY1iX9ArOVaVGFJwUmlAKspzwESnMd9bct1f5G475BolgdOwnhXMExCoRakANz18Z7an23ug3viFB+93DegZaK6xijqOTAPI+ezMHlCpkCVvyigEffEpYBzEfMJF9duOhOMdt2gVtaODbookr51Rdt1ujcsvEVLgzMlzVHmer8XrukUmItU9sBF9wAHK+aZ6O45enDmgaFecjlyWfEckrB1INNnbK68M6AXHO3pBnEfxY1Mlwbsis9bXaysQdhHfnoWlef 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 Fri, Apr 25, 2025 at 03:43:25PM +0800, Kairui Song wrote: > From: Kairui Song > > The following WARNING was triggered during swap stress test with > mTHP enabled: ... > The WARN_ON here is simply incorrect. The refcount here must be at least > the mapcount, not the opposite. Each mapcount must have a corresponding > refcount, but the refcount may increase if other components grab the > folio, which is acceptable. Meanwhile, having a mapcount larger than > refcount is a real problem. > > So fix the WARN_ON condition. > > Fixes: 1da190f4d0a6 ("mm: Copy-on-Write (COW) reuse support for PTE-mapped THP") > Reported-by: Kairui Song > Closes: https://lore.kernel.org/all/CAMgjq7D+ea3eg9gRCVvRnto3Sv3_H3WVhupX4e=k8T5QAfBHbw@mail.gmail.com/ > Suggested-by: David Hildenbrand > Signed-off-by: Kairui Song Reviewed-by: Oscar Salvador -- Oscar Salvador SUSE Labs