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[209.85.167.52]) by smtp.gmail.com with ESMTPSA id k12sm875765lfu.252.2022.01.15.06.23.25 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 15 Jan 2022 06:23:25 -0800 (PST) Received: by mail-lf1-f52.google.com with SMTP id bu18so17086286lfb.5 for ; Sat, 15 Jan 2022 06:23:25 -0800 (PST) X-Received: by 2002:a5d:4575:: with SMTP id a21mr12016883wrc.281.1642256183429; Sat, 15 Jan 2022 06:16:23 -0800 (PST) MIME-Version: 1.0 References: <20220114140222.6b14f0061194d3200000c52d@linux-foundation.org> <20220114220555.kAbhSEmus%akpm@linux-foundation.org> In-Reply-To: <20220114220555.kAbhSEmus%akpm@linux-foundation.org> From: Linus Torvalds Date: Sat, 15 Jan 2022 16:16:07 +0200 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [patch 056/146] mm: rearrange madvise code to allow for reuse To: Andrew Morton Cc: ccross@google.com, Dave Hansen , "Eric W. Biederman" , gorcunov@openvz.org, Johannes Weiner , Hugh Dickins , jan.glauber@gmail.com, John Stultz , Kees Cook , Linux-MM , Mel Gorman , Minchan Kim , Ingo Molnar , mm-commits@vger.kernel.org, Oleg Nesterov , Pekka Enberg , Peter Zijlstra , David Rientjes , Rob Landley , serge.hallyn@ubuntu.com, shli@fusionio.com, Suren Baghdasaryan , Al Viro Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 29EB240002 X-Stat-Signature: zz949wkk7w3xey3y83k6ihza8y9m9oj1 Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=google header.b=YlB4c1nL; spf=pass (imf17.hostedemail.com: domain of torvalds@linuxfoundation.org designates 209.85.167.49 as permitted sender) smtp.mailfrom=torvalds@linuxfoundation.org; dmarc=none X-HE-Tag: 1642256607-679552 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: On Sat, Jan 15, 2022 at 12:06 AM Andrew Morton wrote: > > Speed up fork() by up to 40% by refcounting the anon vma name field. What? No. This doesn't speed up anything at all. The refcounting of the anon-vma name field avoids a 40% regression that comes from adding the field in the first place, but this commit message makes it sound like this series is speeding up fork() by 40%. I don't mind the series, but I absolutely mind these kinds of horribly misleading commit messages. This is literally the first commit in the series - and the series in no way improves performance by 40% in the end, it just first makes it worse, and then fixes the regression. I can speed up any function by a thousand percent - if I'm just allowed to make it horribly slow first, and only count the final speedup win when I remove the overhead of the garbage I added. Linus