From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D6D80F357AD for ; Tue, 24 Feb 2026 14:27:01 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 46A856B008C; Tue, 24 Feb 2026 09:27:01 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 415876B0092; Tue, 24 Feb 2026 09:27:01 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 31AF76B0093; Tue, 24 Feb 2026 09:27:01 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 1F4516B008C for ; Tue, 24 Feb 2026 09:27:01 -0500 (EST) Received: from smtpin11.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id A7489562A6 for ; Tue, 24 Feb 2026 14:27:00 +0000 (UTC) X-FDA: 84479577000.11.C0AAC4C Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf03.hostedemail.com (Postfix) with ESMTP id BE62B20002 for ; Tue, 24 Feb 2026 14:26:58 +0000 (UTC) Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=gXS1Lw+M; spf=pass (imf03.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1771943218; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=EgM7jS0cBg0plUTo1cSHYfPUoVqf2Pvxv925xxsrQ+U=; b=hllSL77Z+TCBxMrbfvuV/QMo5Ure2FUDzYpobJfZ8p0YNlgwpE5TV2+dgOHay4hVzBpmIH Bte7FaDtpHQh8CdqBhaXoFyuJ1pFKZbyPILXQ6sSo5SOuzekqaASh8PtK1GJvWN8D2MraM v4XC1wUDMzpaWONtnGSnzAE2dRQ6wKE= ARC-Authentication-Results: i=1; imf03.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=gXS1Lw+M; spf=pass (imf03.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1771943219; a=rsa-sha256; cv=none; b=OokDXCrKTq6l5X9rJsamiKzNdeP6XlP8I7+iz+aE/2njDSrROvvDiu8KFo3mWNZ3zc0xWK NNKR15yiJJfpclvEEBkL50u7rKtOTViK9uYHSrIXLV4jlI+pEzDjAe1Rspb9d32/45WysC Qtt8BIZmz4fai7hkOmdRHBNIQrRvB0A= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id B482942A35; Tue, 24 Feb 2026 14:26:57 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CE5F9C2BC87; Tue, 24 Feb 2026 14:26:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771943217; bh=BOiJGrddjCxvgWVKKZBDfl4YuYUoUq3aMdjFP3iMbUA=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=gXS1Lw+Mc6aaEqFMUfP7GItdAiZafYoGuZqd98hKKTt7LeEiLpwfgpHCLLdZu0WCm dtmtGZ+nXtammriyfV6va/hmaqHBEZi4JAOAFCB6w92C3WTTKwsfNgawEcaxG5KA8X 0VX8N0LyWtOU55Jbq58G9to3YIZRdQgkA/k6gIL1fp8ccTgiXEdFnSyStjjd8HUwZH sSMDX+M1XyITOZapFtg+14G27OR0wcWujEAuZHFIDagw+GK2QRJOT+3qIonxV2G8kx eEyYZs5QVkSfgZ/SWD/kgeBTyAxd9aq8HJ+fMn6ZgWJdTzCa9q08tv4RWAiaJPUCyy RwUotiblOd9Ig== Message-ID: <10fb20fc-b379-433d-9a08-cc962ab70480@kernel.org> Date: Tue, 24 Feb 2026 15:26:50 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] fork: zero vmap stack using clear_pages() instead of memset() To: Linus Walleij 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 , Ankur Arora References: <20260224-mm-fork-clear-pages-v1-1-184c65a72d49@kernel.org> <2553a75a-6dc8-4295-96b3-58367879751c@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam05 X-Rspam-User: X-Rspamd-Queue-Id: BE62B20002 X-Stat-Signature: 6zkcdnenf933o4ara1rce1igsq8pircy X-HE-Tag: 1771943218-74464 X-HE-Meta: U2FsdGVkX1+x/9ROB3OxMGGJpuMrhUjh/2mUbYL2SG4rrSgi7kxGTyWwgoVsdtSgPrGxbd1/eV3nBD1dJH+K27sD37YV7EZwb9b1hr1jxHSrGzZy1itwAlvmZFJJPfSaXiSowCFN6fR5k2A0I9BT+6DV8cLqJBRqYitvVa03q9iLMUQMnBv3l5yfPXYD4HX97uzdgzkN4xmSXLs6RmdBDHHnPytuslboJGhRrH/FN5PfcfrwZluv+TYkyW6Lq4kVkDmdmi+Y7tSOecvjZv5VLcXZ7AHSA2o3Y0u6lEY4oq9MjwGo/IqMcy0Z8K1vulDE8KMuc47rFTp37pMKMxWgKpuzv3fdFQ/rpT7I3yOmKz++Kc+CagWT69FoMJTrv7COkGCsrAaxHTKu8cEmOxXAykmfgDli1DfzqXOkkYlo2pFecEOVqjcqPGxAQGzlBdcQOPWTjPVw7ZlmirRrCgE7tk4EfoCu7lMdmwQpgmZZoDwffKOfW8r9UC5HpLl1oHXy97VIgodLSVHYx5dT9sK+nAwkyLDwCCNLOqcFbczICqxvmtw2w28wLKwKvjGguChFNuCpCznQDXpvOpa/Tq8HVO1E+XeDTzkl7H3cMcWdXTYamp0pbQQhOR55CBMhvtVk08wK6aoM3TVhkDHd/428MgDg/ZD+BzsJY/atM4lVoSTStq8U427Ca+fdz36FReWqC/UKpkqiPqbpfFLAd8cPvAWUa7qoqmZ+UyDFrACOHatWYXjczRQUSvQMUDdkPxGRRpakyAE4QZrVyPGskczYbkB3LmCIny1jqZPsHRACjoBb0VRhXhp5luwMv3PNofZDqWNCHgo8URMXFs0s+yFglQMxPufeIlgMgyP4kgaomElDKpvRf+SJocrnJ5cHMWrc9HLiunK6cTI2Owj6xjOhT74aAkEq0JW5kFb2DAfLUWKSOSVb+NrloPUApK6MYhIeI1FBBaIiyqR3Viv7pd4 NrkWt7f9 AFdqCEzbJfTTI046wgfYDqDULTIyHeyjAjao3tVsWQHsE+edzRR1+3S1O2J9/x+gr/9f7lEMwrus9zJgpmZEeQhsRCsyLI8V4m+Ea5e2JCWLyk+1x1cZRniLq78LZt/OSqkfzWevD18Jy8xiLR/skS1rJCxrtPrKDoNqRghnfIcO5qFo8X3cu0BEqQfhZxsOjPJHidHCoZM56gmP3Zd5Nu03MFvtEJQ/GPpyeA88m7b7waiP267VnRvZGI5g82X3Aug+QH6KxPexSMmMeDP22ud31xvaKZhkGVpv3SXzpKMkaLD3YmNRk11NWHtAIi2sfclGA47NRGEv4vZ2UymEUMYFvBJ27kdkYOFQh 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 2/24/26 14:53, Linus Walleij wrote: > On Tue, Feb 24, 2026 at 2:21 PM 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=b4/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... I'll note that clear_pages() documents: "When running under preemptible models this is not a problem. Under cooperatively scheduled models, however, the caller is expected to limit @npages to no more than PROCESS_PAGES_NON_PREEMPT_BATCH." We discussed during review that we should probably move that batching logic into clear_pages() at some point. PROCESS_PAGES_NON_PREEMPT_BATCH defaults to 1. I'd assume that handling 3 pages here doesn't make a difference, just pointing it out. CCing Ankur. > > If someone has a good fork performance test running on x86 > and can give this a spin, it'd be great! That would be nice :) -- Cheers, David