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Sun, 08 Jun 2025 11:00:06 +0800 (CST) Message-ID: <41302742-921f-44c3-819d-8ad044a7f206@163.com> Date: Sun, 8 Jun 2025 11:00:05 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] readahead: fix return value of page_cache_next_miss() when no hole is found To: Jan Kara , Andrew Morton Cc: willy@infradead.org, josef@toxicpanda.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Chi Zhiling References: <20250605054935.2323451-1-chizhiling@163.com> <20250605145152.9ae3edb99f29ef46b30096e4@linux-foundation.org> Content-Language: en-US From: Chi Zhiling In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CM-TRANSID:_____wDXX+C1_ERotDS5Gw--.4957S2 X-Coremail-Antispam: 1Uf129KBjvdXoW7XFW8uw4xKr15JFykZrWfGrg_yoWktFb_XF 40y3Z8CFn09FW7Zr4DtrsxKrWDta1UKr15t3y5tr15t395Ca93WF4kAryS9rn7Krn2krZ8 JFy5XFZxKr10gjkaLaAFLSUrUUUUjb8apTn2vfkv8UJUUUU8Yxn0WfASr-VFAUDa7-sFnT 9fnUUvcSsGvfC2KfnxnUUI43ZEXa7IUj3fH5UUUUU== X-Originating-IP: [119.39.12.94] X-CM-SenderInfo: hfkl6xxlol0wi6rwjhhfrp/1tbiTxVmnWhE8d7ARAAAsm X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 4EB251A000D X-Stat-Signature: yce9w5q979jrs8jri5gkzzn8pzif5g7r X-Rspam-User: X-HE-Tag: 1749351627-660543 X-HE-Meta: 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 J5deAk87 qMN7ow4KFLXByk429oGOQ/kJdm4bQVfUch8sBfRDEGdvNY56qMbAs9qYjTsEmoJzNVXYXu6z47m15daH/99B++6Tb0KsoYKKQxT1FXjmJemHBOJ+wz74l/6MMNhVHdebEId5kV8xBlZHTbkDvIuTmIZRdf0iWnDTWJ0W9/4Bw5jcSG4zdb0SNCI7tko+iUOvoGlu6lQSG0iVM4f6uOrqqm45yXBM+dc4g7LMRUjAawcGMI4+y9pS5zdvWyAggFU73btdc1fiSIFKT7p2l46xrJipfFlcyYCvHZvN64fnkk0/Va+xuMTwrEmiOgAHYUjjSj6CfR3yTV69RgMft8VVLHarIG29xFXn85aFAW+hlDmNESOJvDi5tVNIMidU4fd63wxIfExhN0usOpIVoTQpwlM3uHdBv1PjmT5nc78aPfh/A+ahn3PrjHc8lCyo7kLDuSXkPsT41ZUYEi6An9B+yZYvSJBLJWYY87mJi 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 2025/6/6 18:54, Jan Kara wrote: > 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 >>> >> >> 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 TBH, in my simple sequential reading test, I did not see any significant speed improvement.