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Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1t1u0E-0000000DadV-07Lt; Fri, 18 Oct 2024 20:55:18 +0000 Date: Fri, 18 Oct 2024 21:55:17 +0100 From: Matthew Wilcox To: Yosry Ahmed Cc: Kairui Song , linux-mm@kvack.org, Andrew Morton , Johannes Weiner , Nhat Pham , Chengming Zhou , Chris Li , Barry Song , "Huang, Ying" , linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm, zswap: don't touch the XArray lock if there is no entry to free Message-ID: References: <20241018192525.95862-1-ryncsn@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 95E174001F X-Stat-Signature: 8xdfioub186d3ijbif7cuudb4377dptq X-HE-Tag: 1729284912-973513 X-HE-Meta: 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 p5fQohEx 88XENtPKsb2z6bUJQDkLHPV3DvIjQ50wQ3FNsiQ3eB5mAmoXEf+kFNOn0wDKEbHAQqRet8Jpv+3E6NeKOZu6+QkhQXC1oLsaSr3JxUESKfMjRvTeEJ0phQEzQWBhf30gV7yD0peKNZXO25PfS8XB4WF8ElnfT+xFC6+dPSnAxbyKToDCzojVSqhRFrRe9E53TPhgOIhjYs6Tb6qipdFDp5AHXg6jDlg4eIBeEMYJDM8hGgO2PQaPgao/QQIvMjCbe3eLY 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 Fri, Oct 18, 2024 at 01:40:18PM -0700, Yosry Ahmed wrote: > Oh I thought xas_reload() is enough here to check that the entry is > still there after the lock is acquired. Do we have to start the walk > over after holding the lock? Yes. The entry is guaranteed to still be valid, but the node you're looking in might have been freed, so you can't modify the node without making sure the node is still in the tree. We could make that cheaper than a rewalk, but you're going to need to write that code since you're the first to want to do something like this.