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Mon, 06 Feb 2023 01:18:01 -0800 (PST) Date: Mon, 6 Feb 2023 09:17:59 +0000 From: Hao Lee To: Matthew Wilcox Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: eliminate function call overhead during copy_page_range() Message-ID: <20230206091759.GA16477@haolee.io> References: <20230205150602.GA25866@haolee.io> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.12.1 (2019-06-15) X-Rspamd-Queue-Id: D636DC001A X-Stat-Signature: as98p5jj9hxghk7dwfry8k3xfojkfiu7 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1675675082-93185 X-HE-Meta: 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 Fd01doat p/5xhqm0MMUFcbPLyIUHBfWjce/bU4M0EMFTLyUMch3Vk2+1tOo5+zwXhGSDYmHeulsFsMVS+YFqRgMJhHrb2XZUQxR1weWbAJLsdL/BqkD+nVIKjxdNEFSJpKBeFA12BSk3cR2YX4pPq8GnKYJxBptDSQ4oEsM5FIsplma67+9SPkVlWtcjD9GryntI32N04Ir5ZnH554j4YK0VUovbB4xhV9cRORk96DvTygomd9V+vjkaqllrkD3/LGu8PwsBMGQu3oVNz1ltVfDrXpgsiX1yPxaEOxuvy/0w5qFqxOHdrPET0avu/2NlK67j1FsaiuKn/NRh0ROGuy44KI6ZgWu3sLP0pFfX7yJZvP9nTj/PyAyAvNRFN7gZb8f3Jc3tl5niBlkoFNn6bN0k92HfdO1HvA5DVU4EyHZuPcu9dIzgNvs2b1lg4jZqP056TYjQ4rSrZ3ttrRG+rpGg+fcU1c/049A== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000457, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sun, Feb 05, 2023 at 09:53:53PM +0000, Matthew Wilcox wrote: > On Sun, Feb 05, 2023 at 03:06:02PM +0000, Hao Lee wrote: > > vm_normal_page() is called so many times that its overhead is very high. > > After changing this call site to an inline function, copy_page_range() > > runs 3~5 times faster than before. > > So you're saying that your compiler is making bad decisions? What > architecture, what compiler, what version? Do you have > CONFIG_ARCH_HAS_PTE_SPECIAL set? > > Is there something about inlining it that makes the compiler able to > optimise away code, or is it really the function call overhead? Can > you share any perf results? I am so embarrassed; I forgot to disable function_graph when timing the non-inlined function so my test was interfered. And the actual performance improvement is only ~3%. Please ignore this patch. Sorry... >