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b=puq0sL96fJaa3xNR1nc487iLxN+1dcd6txN7K2CR+DoZizhfmCgpe2iHCty476HiP 9FwCoXKv5y5J2Aao/tMOA/pj+ofQVyQoVgQt+1E8j7QkDCgSKausn0TuqW114osSjW iYQQ3UfgymxDFY8R2YhvYG2XKamU9E6ZMmdmRmrU= Date: Mon, 1 Jul 2024 23:22:24 -0700 From: Andrew Morton To: Wei Yang Cc: linux-mm@kvack.org, willy@infradead.org, David Hildenbrand Subject: Re: [PATCH] mm/page_alloc: remove prefetchw() on freeing page to buddy system Message-Id: <20240701232224.43d5243ec9f15aa3e29a7ec5@linux-foundation.org> In-Reply-To: <20240702020931.7061-1-richard.weiyang@gmail.com> References: <20240702020931.7061-1-richard.weiyang@gmail.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: C7F9340017 X-Stat-Signature: d31qfx89xruoqrdwodqzh3oitantzfdm X-Rspam-User: X-HE-Tag: 1719901346-649693 X-HE-Meta: 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 zE0R7m++ 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 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 Tue, 2 Jul 2024 02:09:31 +0000 Wei Yang wrote: > The prefetchw() is introduced from an ancient patch[1]. > > The change log says: > > The basic idea is to free higher order pages instead of going > through every single one. Also, some unnecessary atomic operations > are done away with and replaced with non-atomic equivalents, and > prefetching is done where it helps the most. For a more in-depth > discusion of this patch, please see the linux-ia64 archives (topic > is "free bootmem feedback patch"). > > So there are several changes improve the bootmem freeing, in which the > most basic idea is freeing higher order pages. And as Matthew says, > "Itanium CPUs of this era had no prefetchers." > > I did 10 round bootup tests before and after this change, the data > doesn't prove prefetchw() help speeding up bootmem freeing. The sum of > the 10 round bootmem freeing time after prefetchw() removal even 5.2% > faster than before. I don't think I've ever seen prefetch make a damn bit of difference. > [1]: https://lore.kernel.org/linux-ia64/40F46962.4090604@sgi.com/ > > Signed-off-by: Wei Yang > Suggested-by: Matthew Wilcox > CC: David Hildenbrand > > --- > The patch is based on mm-stable with David's change. Oh help. David makes many changes. Please identify patches with much care. Fully quoting the email title works, as does a link.