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Fri, 11 Aug 2023 19:29:27 -0700 (PDT) MIME-Version: 1.0 References: <20230809045810.1659356-1-yosryahmed@google.com> In-Reply-To: From: Shakeel Butt Date: Fri, 11 Aug 2023 19:29:14 -0700 Message-ID: Subject: Re: [PATCH] mm: memcg: provide accurate stats for userspace reads To: Yosry Ahmed Cc: Michal Hocko , Johannes Weiner , Roman Gushchin , Andrew Morton , Muchun Song , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 216FA4000B X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: zbwd7s83jzudgfar5jjbgtwuuc4bi4ff X-HE-Tag: 1691807367-349328 X-HE-Meta: U2FsdGVkX19nlzNCLCrOGmCpaS+TEdU/Gtv61ffoeALuKlQjv+wHDhMe1Czy2Wp9brFG1KovKVzzKIPi+4pqaF4OuQ5LLtYkiFehVRBYBgoR6NzY21dfcHL0O5npMJA/dyEmykrDoe+AJcskoO8BM+wZq7t/IT9/9A5adcFb6DfduTCXuBAiJYzxj0Ag4xNzASrMhSDdWWb57WJkOszVpxGob2JGfe7GMU4wUgBbn/W1LV6Lgeq8Ov2MrUxunnFVnZM4MP0PoOnbi7NPM80Fq8Yq0Ec0T6w0i5thSIXIdSQmCJaO+GMEu0x7JD+giWvNZtDDwW13UObHxmx8JLnSGCI4siaRglhNipYBV4GzyZQYkAyZ0EWSo93Fz/480kTBcBNty5pzu4KVMLDBkFy/ieg2uYxRjVY3yFxFswzwKhz1TUy37a3xQOLaslikP+epvX6QJwuuR3O03L6QiL5pohAx6P9PjKzWMQdz15luPiMuqUsyahI1WHaFUwXfvQyXSofz+LLoh2oEjIp+JjzLUnMRuQX2/GGzWHjQG8Rm9R5igbyEj+aaWVRLqHwV2AOreX4UUFszoMPKHi8scytN0NtJ1RbNjTplWZsMACwZ91ZSnqnyOnfwmBwBpBqEIXA51okHJpoJHQGyhOd7IlIxInKJxGwSFoJUR+MrbtI5OTvzy6tRRyvZ0HTZa4vZ8nvi8p7q2lYUjveYdhr5RG7Yj6lRAp7QXHPLspMZL7L52vRWOPmExMniMRbbazgRdEOLk2WLBsGCnDycNw4R6iEns+6Dqh/Vydkvrzv0jSz32cMmCFC0Cr2bStIxpEFTrAfFG4HUyZTlPAnIkTKIJtSTE1IBVgFxpoav69g9avVSf+BOBiacTZvnsEGEYQ2ee2IaOEdHyv3n/aqSSYWO7MUmDiueXVpQA/x1WjVAcOlJerwtosQ+H/yJ8ahlHusQ3Qs2e54A6osiw0DP9U8NLuA MLg3pgIR XPfTmkLiDZ1Hf1bm2YGpLlCK3og7Tci7DJBm+eGkx4aSDoeUjvkK8cIaFlHSJauNEt+BG2maDlmd6vlLYFY1GT1IbZvm3HHNmTU2q+8ulN9KKP7ckcQLsrBPFsz4sIy/dKplJ8ynPDTS4IVk2nxFOmDuD1GPZfRo52idugrdZDXueBCbn78EXd9oSGxuKBgl8l1A54ys+HWspxm05Ur/CDevPTSXhYtq/51ZnSUUv6p/0gxfhzkHOClujaA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.021875, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Aug 11, 2023 at 7:12=E2=80=AFPM Yosry Ahmed = wrote: > [...] > > I am worried that writing to a stat for flushing then reading will > increase the staleness window which we are trying to reduce here. > Would it be acceptable to add a separate interface to explicitly read > flushed stats without having to write first? If the distinction > disappears in the future we can just short-circuit both interfaces. What is the acceptable staleness time window for your case? It is hard to imagine that a write+read will always be worse than just a read. Even the proposed patch can have an unintended and larger than expected staleness window due to some processing on return-to-userspace or some scheduling delay.