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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1pIDHF-000EF3-3y; Wed, 18 Jan 2023 18:35:13 +0000 Date: Wed, 18 Jan 2023 18:35:13 +0000 From: Matthew Wilcox To: Hillf Danton Cc: Suren Baghdasaryan , vbabka@suse.cz, hannes@cmpxchg.org, mgorman@techsingularity.net, peterz@infradead.org, hughd@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 41/41] mm: replace rw_semaphore with atomic_t in vma_lock Message-ID: References: <20230109205336.3665937-42-surenb@google.com> <20230116140649.2012-1-hdanton@sina.com> <20230117031632.2321-1-hdanton@sina.com> <20230117083355.2374-1-hdanton@sina.com> <20230118062639.2839-1-hdanton@sina.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230118062639.2839-1-hdanton@sina.com> X-Rspamd-Queue-Id: CCCA580005 X-Stat-Signature: ona1jnh9hnp7f9cgdfbbmqddb5gdqi5t X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1674066930-398930 X-HE-Meta: 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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: On Wed, Jan 18, 2023 at 02:26:39PM +0800, Hillf Danton wrote: > On Tue, Jan 17, 2023 at 10:27 AM Matthew Wilcox wrote: > > > > The cpu_relax() is exactly the wrong thing to do here. See this thread: > > https://lore.kernel.org/linux-fsdevel/20230113184447.1707316-1-mjguzik@gmail.com/ > > If you are right, feel free to go and remove every cpu_relax() under the > kernel/locking directory. I see you didn't read the whole thread where Linus points out that a cmpxchg() loop is fundamentally different from a spinlock.