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[209.85.167.47]) by smtp.gmail.com with ESMTPSA id p20-20020a2ea4d4000000b0024f3d1daeabsm1775030ljm.51.2022.05.04.14.10.09 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 04 May 2022 14:10:09 -0700 (PDT) Received: by mail-lf1-f47.google.com with SMTP id p12so4430388lfs.5 for ; Wed, 04 May 2022 14:10:09 -0700 (PDT) X-Received: by 2002:a05:6512:b12:b0:44a:ba81:f874 with SMTP id w18-20020a0565120b1200b0044aba81f874mr15971597lfu.449.1651698608781; Wed, 04 May 2022 14:10:08 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Linus Torvalds Date: Wed, 4 May 2022 14:09:52 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [patch 02/14] tmpfs: fix regressions from wider use of ZERO_PAGE To: Borislav Petkov Cc: Mark Hemment , Andrew Morton , "the arch/x86 maintainers" , Peter Zijlstra , patrice.chotard@foss.st.com, Mikulas Patocka , Lukas Czerner , Christoph Hellwig , "Darrick J. Wong" , Chuck Lever , Hugh Dickins , patches@lists.linux.dev, Linux-MM , mm-commits@vger.kernel.org, Mel Gorman Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 199B81C0011 X-Stat-Signature: 5y69119wb9r1bqybz9q41efnsn8hbj8g X-Rspam-User: Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=google header.b="G/uHV4KH"; spf=pass (imf21.hostedemail.com: domain of torvalds@linuxfoundation.org designates 209.85.167.45 as permitted sender) smtp.mailfrom=torvalds@linuxfoundation.org; dmarc=none X-HE-Tag: 1651698606-931128 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 Wed, May 4, 2022 at 2:01 PM Borislav Petkov wrote: > > I could try to do a perf probe or whatever fancy new thing we do now on > clear_user to get some numbers of how many times it gets called during > the benchmark run. Or do you wanna know the callers too? One of the non-performance reasons I like inlined memcpy is actually that when you do a regular 'perf record' run, the cost of the memcpy gets associated with the call-site. Which is universally what I want for those things. I used to love our inlined spinlocks for the same reason back when we did them. Yeah, yeah, you can do it with callchain magic, but then you get it all - and I really consider memcpy/memset to be a special case. Normally I want the "oh, that leaf function is expensive", but not for memcpy and memset (and not for spinlocks, but we'll never go back to the old trivial spinlocks) I don't tend to particularly care about "how many times has this been called" kind of trace profiles. It's the actual expense in CPU cycles I tend to care about. That said, I cared deeply about those kinds of CPU profiles when I was working with Al on the RCU path lookup code and looking for where the problem spots were. That was years ago. I haven't really done serious profiling work for a while (which is just as well, because it's one of the things that went backwards when I switch to the Zen 2 threadripper for my main machine) Linus