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[109.81.89.112]) by smtp.gmail.com with UTF8SMTPSA id 5b1f17b1804b1-450d800658csm13986585e9.27.2025.05.30.03.23.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 30 May 2025 03:23:45 -0700 (PDT) Date: Fri, 30 May 2025 12:23:44 +0200 From: Michal Hocko To: Aboorva Devarajan Cc: Baolin Wang , akpm@linux-foundation.org, david@redhat.com, shakeelb@google.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH] mm: fix the inaccurate memory statistics issue for users Message-ID: References: <3dd21f662925c108cfe706c8954e8c201a327550.1747969935.git.baolin.wang@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: E9C67A0008 X-Stat-Signature: 7754bdt9rmfdqen6khcge8wwqf997bpt X-Rspam-User: X-Rspamd-Server: rspam07 X-HE-Tag: 1748600627-507570 X-HE-Meta: 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 FJdk0iWC strRltfc5iwwXnvFCIL8LD5pp7c+Vbtw+mgwM92fm688U2A5HIE4GXCF8jml6Aar7oKKgsql481v9aW5ij6ks6bgaTRTeSiUJusNvupp1Jhg+tHiUxOJfwrA7VeHAV7QZm/bYldb9i+u9Tfv1DZG0kD2RDA8dqPXhmftwyyXZ5XNA6nBvonqOGbuVs0vdOB1KHf6ELRQdJrQyHpaRM0KMc9HudLOTw1ogMdcYQBA/vojOpo9eOTTyx/JY05/CrTUuJ54A/Jj4F/M/2jM6ZUPpIKQIrlvHuvSVlp/1jz0wsfg5qma1enwjlDhcuUbNrJfgMSNi 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 23-05-25 15:44:37, Aboorva Devarajan wrote: > While this change may introduce some lock contention, it only affects > the task_mem function which is invoked only when reading > /proc/[pid]/status. Since this is not on a performance critical path, > it will be good to have this change in order to get accurate memory > stats. This particular function might not be performance critical but you are exposing a lock contention to the userspace that could be abused and cause contention controlled by unprivileged user. I do not think we want that without any control. Or is the pcp lock not really affecting any actual kernel code path? So while precision is nice it should be weight against potential side effects. -- Michal Hocko SUSE Labs