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b=f4V/mmed9e0YDLLfKFUI3gTfxXB+JpN3LMoEqFnAC7hyVjTHQrCGunNiHXub4D6ij sqo6cmx5ENyWIptgpIEDkDumf6RZI6ZpznLpBppwlfWIsXF701XkUacB3hS5YBLjJH uiGS0hn9qFDnBqZNfb12me35OHPWH2AuvWNKbx4bKPrwsx8yrDmt88Rke6ysw3cqrL 2TAoNGiSIQtknqHBm+plM8WaPMd3Y4+J33fLDFotZhb3iOVtYmTTevVYBf/GS5wfPg ZJKkRT5vZZgaMF5xeH2t2VQa6T7nTa1l0sHOqZ36JilBgzEvXvw5Gj5NEbhcb7bj2t eIC1YI88wpZNQ== Received: by mail-yx1-f54.google.com with SMTP id 956f58d0204a3-64aedd812baso5084913d50.3 for ; Tue, 24 Feb 2026 05:53:35 -0800 (PST) X-Forwarded-Encrypted: i=1; AJvYcCVYjwKfXxHDgf2FGZ7T00nnfMRRijHRwA13D5PaNZ5FNLfIcHdscheP+pCJpPzEywEL062uQu85zg==@kvack.org X-Gm-Message-State: AOJu0YxROHHSffDxknAeAZsbnhW2DwOrCFFYVKGztVYYt41n3C3mt0mI 3Bk6KYdpCE5cg2H5AeoD17QhRsmT9KZkeszdUjm7kJr/NgeCRLUzTYOOqnvklmDAHSaJW8ueQAg BNuuvMnU1kje4ffqIdvW2wGoeU5E6eVY= X-Received: by 2002:a05:690e:d5a:b0:64c:973e:874a with SMTP id 956f58d0204a3-64c974dca95mr3429415d50.42.1771941214411; Tue, 24 Feb 2026 05:53:34 -0800 (PST) MIME-Version: 1.0 References: <20260224-mm-fork-clear-pages-v1-1-184c65a72d49@kernel.org> <2553a75a-6dc8-4295-96b3-58367879751c@kernel.org> In-Reply-To: <2553a75a-6dc8-4295-96b3-58367879751c@kernel.org> From: Linus Walleij Date: Tue, 24 Feb 2026 14:53:23 +0100 X-Gmail-Original-Message-ID: X-Gm-Features: AaiRm53tb2rvqaot7mvXTxtm6mGGNPobUyruddK7Z4F9nhs9QdcbYdTorcT5uzM Message-ID: Subject: Re: [PATCH] fork: zero vmap stack using clear_pages() instead of memset() To: "David Hildenbrand (Arm)" Cc: Kees Cook , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-mm@kvack.org, Mateusz Guzik , Pasha Tatashin Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: DA0F214000C X-Stat-Signature: qqk5wdqeggy84i8wd3oed7zci7ysg54k X-HE-Tag: 1771941215-841089 X-HE-Meta: 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 VAF83/dN vM9EplNXBLAzSISPzUiiSChgFaLb9cSTrmg2uPaXYIeETD01jRTCzwe00sr+HTvwd7GbwvIZZ/1JfC/teSsqdKr1UW8ZGk28WBh5GbJuYfn7rQO9++RMgYKRNsY7gDl6qY4wHjp6aIP3IvxbN4osRtXFGktqu9fptlwAcwlD/13x8pw9cVO+Q8UuRQAB6gxomDpcfwSw+cOY9fSAeNMwE0ifwrYXQMZQ+FeGh62U1oi9R0l+7t4XhiQwSSBak10p+IPttPzMEuPa91fK7ML2+TK0vGLKVOi/v/EMBp/+4vctBy0lRk640016FW5PM9OhvQWBrk4gHLivWRIerVS7VV1LuUL6b7XNwzpi5 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 Tue, Feb 24, 2026 at 2:21=E2=80=AFPM David Hildenbrand (Arm) wrote: > On 2/24/26 11:26, Linus Walleij wrote: > > After the introduction of clear_pages() we exploit the > > fact that the process vm_area is allocated in contiguous > > pages to just clear them all in one swift operation. > > The pages are virtually contiguous (vmalloc IIUC), not necessarily > physically contiguous. For clear_pages() that should work. Yeah that's what I meant with contiguous, sorry. > > /* Clear stale pointers from reused stack. */ > > - memset(stack, 0, THREAD_SIZE); > > + clear_pages(vm_area->addr, vm_area->nr_pages); > > LGTM. > > Do we have any idea about performance impact etc? I have a pending patch for implementing clear_pages() for arm64, https://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-integrator.git= /log/?h=3Db4/aarch64-clear-pages which is in a performance test loop, once I get baseline data from that I can test something fork-intensive (hackbench, I guess) with this patch on= top. So making that patch made me remember this one code site... If someone has a good fork performance test running on x86 and can give this a spin, it'd be great! Yours, Linus Walleij