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AJvYcCXtmJ/FjNC6nhpxiodoowktC2ODnXwKXCLKCVOZjX0RhXxgkVkYwOw+CmTPcGpOzIpzExJzTJ31IA==@kvack.org X-Gm-Message-State: AOJu0YwglVBrW1Ymg/qlghVl/LxaP+pv/1uZTKu35oNcbBlzwRfiv9e1 KKHRcFs2YNrR+wRqHcE4e4G7vXFXDGRVu68n2TrSEHi/VNSJjOgg00bIzynrCS982IgGFTePTat E9CDfGTMLWSrsW8VoRxQm96WSWzKuKPIS8t6f X-Google-Smtp-Source: AGHT+IF4inkPL/SJ30v3SbeY+JGZUjMhFuq8i617wBTVyk6lj63eDWWcBGgSSt4FuO5YRr0sRkemoRQbhu0WaQlhF1k= X-Received: by 2002:a17:907:72cf:b0:a9a:55db:85de with SMTP id a640c23a62f3a-a9a69772b23mr324735166b.9.1729285253987; Fri, 18 Oct 2024 14:00:53 -0700 (PDT) MIME-Version: 1.0 References: <20241018192525.95862-1-ryncsn@gmail.com> In-Reply-To: From: Yosry Ahmed Date: Fri, 18 Oct 2024 14:00:16 -0700 Message-ID: Subject: Re: [PATCH] mm, zswap: don't touch the XArray lock if there is no entry to free To: Matthew Wilcox 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: E9CA220020 X-Stat-Signature: r3oj1t7ynw7wtytq6n5niw1c59qr4umu X-Rspam-User: X-HE-Tag: 1729285243-100696 X-HE-Meta: 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 hCbpM7HR WjjkZKg0xStXqAmUTQPjusk+3Oq1hWSvlQgF856SOKbbjNqDm5X38PBJVshyROYEptLPoqpiXVCG9n8RP8jGSYXmFWnUC/JJlUCNZ3IBuTXFO4Li1LCn+tPQFDS2tqYhtg3Uhxp1BeOLNeKpW8dGB/LO6z83xANBfDhXlAokTZNnbWtpUN2tLn1J41sSLpGL0NWqBgilTGrWjrRhWP1d9uPcDDLs5qFrLtcezelLF+XW+VLuUtWz8miTRMA1wmPQVXtTJq8EitillRKgyQXYTeLpc/rnvNBmNSCPv/qmpjL7hx26lb5+VSBMl3Rqizh/ioDdh5HAZUyTv51U= 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 1:55=E2=80=AFPM Matthew Wilcox wrote: > > 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. I see, thanks for elaborating. Could you confirm if the current patch with the xas_reset() added would be equivalent to just checking xa_load() before using xa_erase()?