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([103.163.65.25]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7fe1427026dsm1595735b3a.46.2025.12.17.23.25.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 17 Dec 2025 23:25:52 -0800 (PST) From: Dipendra Khadka To: hannes@cmpxchg.org Cc: akpm@linux-foundation.org, mhocko@kernel.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/memcg: reorder retry checks for clarity in try_charge_memcg Date: Thu, 18 Dec 2025 07:25:41 +0000 Message-ID: <20251218072543.5071-1-kdipendra88@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20251215204624.GE905277@cmpxchg.org> References: <20251215204624.GE905277@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 0EDE018000B X-Stat-Signature: kymf6wejuexhi5oiwxhsxcr7jt6hg63z X-Rspam-User: X-HE-Tag: 1766042753-164176 X-HE-Meta: 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 CwG224gi mbnzlQLQCx/lbNT0b+b1TOhFcfXlTiLjbRT3rvrk1tQr8zOczOMwWQa1VkM3RqmWBUZ9rIAftimbmW+X9yi8ngdt4tX4jBz4o+qSkyEFqp8t0a3PSbx/rxqBGpANyK6VSDXxPO2P5q4dxs55vUL5D0ahHbkazOH6u3pv7o3zSjvVFNi97PwB4FRSyVh30FgKZHk51UH2+DfCuiI7DoaiWSRsx2kCYYpC9FKXjSrldtOdeInzW+7RuvwfO2RPZXMg5/UHZo+4ngW2Qc/7gZ347JNAt8a0dOtLLGaOWqf6E6poi8GLLIXtW0rNznuSue+fsyXrKa2MGzjegbBXfZV7M4fbv1tinzN18mEtaKlFfnwN2F2IkxQLUmBbnk9JF+wHtsibo9l18xYVYmnyjZac7tQr5mrppXfKxtGCn+dnhMH2SGPApZc5ZFdtJ1Hn4RC35JnoqK+PyRLEsi5b1s8x5AjquYA== 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: Hi Johannes, Thank you for the feedback. Let me clarify the scenario this patch addresses. The task_is_dying() check in try_charge_memcg() identifies when the CURRENT task (the caller) is the OOM victim - not when some other process was killed. Two scenarios: 1. Normal allocator triggers OOM: - Process A allocates → triggers OOM - Process B is killed (victim) - Process A continues with reset retries - task_is_dying() = false for A → Unchanged by my patch 2. Victim tries to allocate: - Process B (victim, TIF_MEMDIE set) tries to allocate - task_is_dying() = true - Current code: wastes retries on hopeless reclaims - My patch: exits immediately → Optimization for this case The victim has three safety mechanisms that make the retries unnecessary: 1. oom_reaper proactively frees its memory 2. __alloc_pages_slowpath() grants reserves via oom_reserves_allowed() 3. Critical allocations with __GFP_NOFAIL still reach force: label The retry loop for a dying victim is futile because: - Reclaim won't help (victim is being killed to free memory!) - Victim will exit regardless - Just wastes CPU cycles Would you like me to provide evidence showing the unnecessary retries, or run specific tests to verify the safety mechanisms are sufficient? Best Regards, Dipendra