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Mon, 27 Jan 2025 16:29:53 -0800 (PST) Received: from google.com ([2401:fa00:8f:203:566d:6152:c049:8d3a]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2f7ffa83b24sm8725429a91.46.2025.01.27.16.29.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 27 Jan 2025 16:29:53 -0800 (PST) Date: Tue, 28 Jan 2025 09:29:47 +0900 From: Sergey Senozhatsky To: Uros Bizjak Cc: Sergey Senozhatsky , Andrew Morton , Minchan Kim , Johannes Weiner , Yosry Ahmed , Nhat Pham , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 2/6] zsmalloc: make zspage lock preemptible Message-ID: <6f3mkwaehrrcpekezlryfipc7dw3vxovdlvybt4utfqpmonywl@n5vm4vnx5jrn> References: <20250127080254.1302026-1-senozhatsky@chromium.org> <20250127080254.1302026-3-senozhatsky@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 137DE80010 X-Stat-Signature: 4ekfzcwkre4b5fpfufd85f416iu65umj X-Rspam-User: X-HE-Tag: 1738024194-79308 X-HE-Meta: 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 5zqQeH7Z JuU5C6TlXB7zkVSqnABO1Dabkg8SgaUoJ5ZSoyE/OuHJkkEFTkpboeD6kmw8phJ+ynep5n3B8jNZiOBYAQu5ofHoPRNdmIAaZCDyJP1dLOQK2BkLkuJN6mHLgvq+XRm7QlXGb6+3EPa55XZyNrFMVC7P583sdV9T2hEpAycQMpE0fCednq/qiD9L0+OaljTJvXMEVXUwl0C0dTdYyG+goZwtUGng6R4MGrLdgF7LyQTmQ1ooENbNr8LSGDcsQAnsG6qDIhNLdKtgfoiNroaYbQi+oTSj9RHZtg3k+Su9gIfM0nIvbcJcNM8h9fNZ4U+SnQjNnWzHNzp6QLuEN9jHtbziPIsMg73j3ALTUq10QIAktm5s= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000075, 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 (25/01/27 21:23), Uros Bizjak wrote: > > +static void zspage_read_lock(struct zspage *zspage) > > +{ > > + atomic_t *lock = &zspage->lock; > > + int old; > > + > > + while (1) { > > + old = atomic_read(lock); > > + if (old == ZS_PAGE_WRLOCKED) { > > + cpu_relax(); > > + continue; > > + } > > + > > + if (atomic_cmpxchg(lock, old, old + 1) == old) > > + return; > > You can use atomic_try_cmpxchg() here: > > if (atomic_try_cmpxchg(lock, &old, old + 1)) > return; > > > + > > + cpu_relax(); > > + } > > +} > > + > > +static void zspage_read_unlock(struct zspage *zspage) > > +{ > > + atomic_dec(&zspage->lock); > > +} > > + > > +static void zspage_write_lock(struct zspage *zspage) > > +{ > > + atomic_t *lock = &zspage->lock; > > + int old; > > + > > + while (1) { > > + old = atomic_cmpxchg(lock, ZS_PAGE_UNLOCKED, ZS_PAGE_WRLOCKED); > > + if (old == ZS_PAGE_UNLOCKED) > > + return; > > Also, the above code can be rewritten as: > > while (1) { > old = ZS_PAGE_UNLOCKED; > if (atomic_try_cmpxchg (lock, &old, ZS_PAGE_WRLOCKED)) > return; > > + > > + cpu_relax(); > > + } > > +} > > The above change will result in a slightly better generated asm. Thanks, I'll take a look for the next version.