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b=A+ne60EMDGAtb60eZdI0y7RDRg Zs0yglbxoVjo/fqdy5mmectp8PZOH1L4sSAMkifhKh3eM8JRETpaSuIAoe4GhKhB0pgXkDsjv8cgq uqRrUqJ+UBCit+KdB9BlbK8BusH2NpOYvXAklfXNkyW6TVtD3FgbBcbxJNdpzO4y81H0kuVS25KkR YJNB9i47Uoe4ArK5ILkCylpnE2hh6KdAnOYeYmqBZHphVkeQs3NQtWU775xNcxYKdO5Xvl4esyA9x 6WznY9A9aIYR1ilzdnyD5qF8U+u4uEt2cbUgM7AqhNyhbop8WmXlSPL8AiwmIR/Qlo3w8PnO8gTPS uvs3OdQA==; Received: from fangorn.home.surriel.com ([10.0.13.7]) by shelob.surriel.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.97.1) (envelope-from ) id 1vgZYt-000000003Ph-11qy; Thu, 15 Jan 2026 21:27:44 -0500 Message-ID: <2cab00c18ed7499e5ef143c7f3198c61d56ede25.camel@surriel.com> Subject: Re: [v3 PATCH 1/1] fs/proc: Expose mm_cpumask in /proc/[pid]/status From: Rik van Riel To: Aaron Tomlin , Dave Hansen Cc: "David Hildenbrand (Red Hat)" , oleg@redhat.com, akpm@linux-foundation.org, gregkh@linuxfoundation.org, brauner@kernel.org, mingo@kernel.org, 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" Date: Thu, 15 Jan 2026 21:27:44 -0500 In-Reply-To: References: <20260115205407.3050262-1-atomlin@atomlin.com> <20260115205407.3050262-2-atomlin@atomlin.com> <4a1c24ae-29b0-4c3e-a055-789edfed32fc@kernel.org> <6531da5d-aa50-4119-b42e-3c22dc410671@intel.com> Autocrypt: addr=riel@surriel.com; 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charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 (3.56.2-2.fc42) Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Thu, 2026-01-15 at 20:53 -0500, Aaron Tomlin wrote: >=20 > Based on my reading of arch/x86/mm/tlb.c, the lifecycle of each bit > in > mm_cpumask appears to follow this logic: >=20 > =C2=A0=C2=A0=C2=A0 1. Schedule on (switch_mm): Bit set. > =C2=A0=C2=A0=C2=A0 2. Schedule off: Bit remains set (CPU enters "Lazy" mo= de). > =C2=A0=C2=A0=C2=A0 3. Remote TLB Flush (IPI): > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 - If Running: Flush TLB, bit remains= set. > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 - If lazy (leave_mm): Switch to init= _mm, bit clearing is > deferred. > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 - If stale (mm !=3D loaded_mm): bit = is cleared immediately > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 (effectively the second = IPI for a CPU that was previously > lazy). >=20 You're close. When a process uses INVLPGB, no remote TLB flushing IPIs will get sent, and CPUs never get cleared from the mm_cpumask. --=20 All Rights Reversed.