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Fri, 6 Jun 2025 10:54:16 +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 CsJ/B9jIQmh8OQAAD6G6ig (envelope-from ); Fri, 06 Jun 2025 10:54:16 +0000 Received: by quack3.suse.cz (Postfix, from userid 1000) id D02D0A0951; Fri, 6 Jun 2025 12:54:15 +0200 (CEST) Date: Fri, 6 Jun 2025 12:54:15 +0200 From: Jan Kara To: Andrew Morton Cc: Jan Kara , Chi Zhiling , willy@infradead.org, josef@toxicpanda.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Chi Zhiling Subject: Re: [PATCH] readahead: fix return value of page_cache_next_miss() when no hole is found Message-ID: References: <20250605054935.2323451-1-chizhiling@163.com> <20250605145152.9ae3edb99f29ef46b30096e4@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250605145152.9ae3edb99f29ef46b30096e4@linux-foundation.org> X-Rspamd-Queue-Id: 518451C0002 X-Stat-Signature: ki1ia8fi34j5wuf81r6t66zhz85osp4h X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1749207258-432286 X-HE-Meta: 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 maPVq2fX urW4WOu9NVDCixDULJ0WunDI6Zt8TRRXTpf8e9BTeoCGJ/+t+82lqXFbAq5dig01hPwFnQisoXinC7fhEfx8/qsz9mmcMoJTgXifnuXD9OX1u8LuiQ34jgVJg++ivyOJyBPQ3txsBDuQccOL2AIx3MQzmeA+PXiD2z2L6LNsZbWOQL43gDDVkmk8Z0/0NAyS3O1PRZpAR2vl4eo7c7U6yVfYjqcjYIwPAlieoOJA0ps6kAO8Xp+d+Tx27WlNj7n3qze+saHqguGwPPp6BttDg/HbcmEpDFrEErkjMWDUck/83taTl+yqe7P9kmtfaIDaTvOwHBbhGrDc1GcSu+TaZYBG/zlzeb3Hp+tq6Iqi1EIf46RA+cHeEhpU8vyelv8dOqJYHkqTuuaf7goh6ph2FWa8c8pLpYrHJGXZWrP+tZRochug= 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 Thu 05-06-25 14:51:52, Andrew Morton wrote: > On Thu, 5 Jun 2025 10:22:23 +0200 Jan Kara wrote: > > > On Thu 05-06-25 13:49:35, Chi Zhiling wrote: > > > From: Chi Zhiling > > > > > > max_scan in page_cache_next_miss always decreases to zero when no hole > > > is found, causing the return value to be index + 0. > > > > > > Fix this by preserving the max_scan value throughout the loop. > > > > > > Fixes: 901a269ff3d5 ("filemap: fix page_cache_next_miss() when no hole found") > > > Signed-off-by: Chi Zhiling > > > > Indeed. Thanks for catching this. Don't know how I missed that. Feel free > > to add: > > > > Reviewed-by: Jan Kara > > > > Thanks. It's a simple patch - do we expect it to have significant > runtime effects? I'm not sure if Chi Zhiling observed some practical effects. From what I know and have seen in the past, wrong responses from page_cache_next_miss() can lead to readahead window reduction and thus reduced read speeds. Honza -- Jan Kara SUSE Labs, CR