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X-CSE-ConnectionGUID: R3ZsNPVkSAmqt3NOGs0RrQ== X-CSE-MsgGUID: YN0eWx0hSAeGa4+ETaSc4Q== X-IronPort-AV: E=McAfee;i="6800,10657,11672"; a="69734210" X-IronPort-AV: E=Sophos;i="6.21,229,1763452800"; d="scan'208";a="69734210" Received: from fmviesa004.fm.intel.com ([10.60.135.144]) by fmvoesa111.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Jan 2026 13:39:29 -0800 X-CSE-ConnectionGUID: Jj7BohohScKkaQuAWSBh0g== X-CSE-MsgGUID: 5hGf53zFQaCARzJNv6HrqA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.21,229,1763452800"; d="scan'208";a="209925131" Received: from cmdeoliv-mobl4.amr.corp.intel.com (HELO [10.125.111.74]) ([10.125.111.74]) by fmviesa004-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Jan 2026 13:39:28 -0800 Message-ID: <6531da5d-aa50-4119-b42e-3c22dc410671@intel.com> Date: Thu, 15 Jan 2026 13:39:27 -0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [v3 PATCH 1/1] fs/proc: Expose mm_cpumask in /proc/[pid]/status To: "David Hildenbrand (Red Hat)" , Aaron Tomlin , oleg@redhat.com, akpm@linux-foundation.org, gregkh@linuxfoundation.org, brauner@kernel.org, mingo@kernel.org Cc: neelx@suse.com, sean@ashe.io, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Dave Hansen , Andy Lutomirski , Peter Zijlstra , "x86@kernel.org" References: <20260115205407.3050262-1-atomlin@atomlin.com> <20260115205407.3050262-2-atomlin@atomlin.com> <4a1c24ae-29b0-4c3e-a055-789edfed32fc@kernel.org> Content-Language: en-US From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 1/15/26 13:19, David Hildenbrand (Red Hat) wrote: > On 1/15/26 21:54, Aaron Tomlin wrote: >> This patch introduces two new fields to /proc/[pid]/status to display the >> set of CPUs, representing the CPU affinity of the process's active >> memory context, in both mask and list format: "Cpus_active_mm" and >> "Cpus_active_mm_list". The mm_cpumask is primarily used for TLB and >> cache synchronisation. I don't think this is the kind of thing we want to expose as ABI. It's too deep of an implementation detail. Any meaning derived from it could also change on a whim. For instance, we've changed the rules about when CPUs are put in or taken out of mm_cpumask() over time. I think the rules might have even depended on the idle driver that your system was using at one time. I think Rik also just changed some rules around it in his INVLPGB patches. I'm not denying how valuable this kind of information might be. I just don't think it's generally useful enough to justify an ABI that we need to maintain forever. Tracing seems like a much more appropriate way to get the data you are after than new ABI. Can you get the info that you're after with kprobes? Or new tracepoints?