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Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1tC39V-00000000JAf-0LVg; Fri, 15 Nov 2024 20:42:49 +0000 Date: Fri, 15 Nov 2024 20:42:48 +0000 From: Matthew Wilcox To: Linus Torvalds Cc: Luis Chamberlain , Al Viro , lsf-pc@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-mm , Daniel Gomez , Pankaj Raghav , Jens Axboe , Dave Chinner , Christoph Hellwig , Chris Mason , Johannes Weiner Subject: Re: [LSF/MM/BPF TOPIC] Measuring limits and enhancing buffered IO Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 122E3180021 X-Stat-Signature: ekas8kgrjesks1mpc6jjpddrhz9r1bq1 X-Rspam-User: X-HE-Tag: 1731703369-371537 X-HE-Meta: U2FsdGVkX184o2p2OTgi0G8EBHyp9ao7U2uzxumjIm32FzD9bK2qIf6QRW8Nc2jLdeGSa4LRdXrGZld2qG/yI5Ht0s9UrU1+V4rT9GB+kH1uco6uncesO7HLJxxg9VPU+VidoJTwmwTzUoSaeuF9JPjq5Btuid7QmCKRXQ4iI2+df5PohHti9ibAPR3mWFven59hDgwaOBaqR1A9TOL2/AHeBTx323ueZZ/3lK8m9ticKnSVbOYZzfkWFHkqi2ePOXT4z4dRN2Njr7RDnFyG8YUH9pckXhQdaSh+1ax/kFNTT7wWXf8kOYhRmoORgSBnzj1B2PV7ro/zWrWdkryUN+xKySBHelEvBid5g2kmbYJ/AIgyWc41PM0pHsXRp+DO3h4pE2U0E07W0/yhiqCNTmXOiUKb3ZtA9+eAaIJw1ZXiD8RZ7MaoBY5G6Hhf2Y3kwiUWuhmLFCfB1/rEMdrt1iZwrAiiMpr9wMeGKORB1rnp1PrB3iC8Jhiwj+yeh0FxX07ues+CXXoSxMMEE/O9oMSxYeCuBZpbep3EFfUDxQQbAHCtJ8bvvTcKCZiBa0iWSD1ZPQm/p+g7S5BtVzddFya2tvosQ25Krzc3SIIH6z12guCxz9EndRDNC38IwEtYurMaq/RbwrE91eQIJYmUVg40S4vsSgP1cKMookdTxxmOQCxdfHxBMBBLBUKylUE+D6DoSxlZO0BsUosl1vbf3yl/SCr6YagmJd/3Qwg3EaIC3bZDROamwpLi7Vd4s3n1OC8ECNftMRPeHIKUEb5gVEwwybz/hY5lvfN4LKuuaSWhEFRqzPU/FHS9w7UtQSu4hTzCNW6lzYUlltRiwn/PX9id3picNME/NT8lCzwv5DQleQiFfkHxlmVLAvazupGZ/x26MAHbkbT7f6WPXbUsNRdHKIsIolF38fp7oDwF3LFDz9vE3/SgRztJvQi2tibI+zVy2wa9TMVn3ypRxej kaToGu+5 yqExJGkgdAyIK6pzI0St8p3hsG7l47FS1mvTrRjNUuIV1InTUuq602N+A7B5biWTI74o1gdjefIyl71b7W/235aRem93+e25kvRSQZfXMlTDCRrJvO+diwnxHiPyYWXcXcLNPwCo8zH2yCbZMdE0kdXgFdYFv1zEEOgWEf/E/faQFoPbmxfAsyJXxeDC+06qZXOxUmadGx5pK4jOKdLMXQGHWqRQoxDM8TJwe1N3TjVMXL2M= 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, Nov 15, 2024 at 11:43:10AM -0800, Linus Torvalds wrote: > And I did find that the "do small reads entirely under RCU" didn't > test for one condition that filemap_get_read_batch() checked for: the > xa_is_sibling() check. I don't think you need it: xas_load: entry = xas_descend(xas, node); xas_descend: while (xa_is_sibling(entry)) { entry = xa_entry(xas->xa, node, offset); so I don't think xa_is_sibling() can ever be true here. xas_next() can return a sibling entry, so it does need the extra check.