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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1ufKbz-0000000E1ua-39Sk; Fri, 25 Jul 2025 15:45:32 +0000 Date: Fri, 25 Jul 2025 16:45:31 +0100 From: Matthew Wilcox To: Xiaole He Cc: Andrew Morton , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v1] mm/readahead: Optimize nr_to_read boundary check Message-ID: References: <20250725152834.7602-1-hexiaole1994@126.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250725152834.7602-1-hexiaole1994@126.com> X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 9D461120007 X-Stat-Signature: a6abzsmimmnxc3pzqz6z9tdnx3x9587h X-HE-Tag: 1753458335-195171 X-HE-Meta: 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 jpHwFMtC PwMjYvJBRcaYu4OufVinnwryfo8LBWI+csGk5CQjTk9K3VNlJlKJ1vqQyQIQ8I/cBWMVSrbJDR3WNIoYue7K+ycpcppJ7gmcB7YvtrHk07aRvgW/0gmDAu6muJ+vuTJfRE3cNn1TTniZ24QwttbFoMti6K5kh6eiM++FZN8Xmk3oKGNZKsExyL+/PGrTCdjex5RFexHXdLA/OA980x+Als/5dh0MYxhdxq1z4 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, Jul 25, 2025 at 11:28:34PM +0800, Xiaole He wrote: > If nr_to_read is, for instance, 3, and end_index - index + 1 is also 3 > (meaning 3 pages remain), the condition 3 > 2 evaluates to true, leading > to nr_to_read being assigned 3 again. While compilers might optimize > this trivial self-assignment, it introduces unnecessary logical overhead > and reduces code clarity. But it makes the initial comparison more complex (by one operation) and I bet you can't measure the difference anyway. I'm not inclined to tweak this.