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 C73E7C5B572 for ; Tue, 11 Aug 2026 16:52:35 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id CAF636B00A9; Tue, 11 Aug 2026 12:52:34 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id C86C36B00AA; Tue, 11 Aug 2026 12:52:34 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B76B56B00AB; Tue, 11 Aug 2026 12:52:34 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 925EB6B00A9 for ; Tue, 11 Aug 2026 12:52:34 -0400 (EDT) Received: from smtpin04.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 34EDBA0CB1 for ; Tue, 11 Aug 2026 16:52:34 +0000 (UTC) X-FDA: 85089582228.04.D809DA5 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf07.hostedemail.com (Postfix) with ESMTP id 805114000C for ; Tue, 11 Aug 2026 16:52:32 +0000 (UTC) Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=Jvgo3kgj; spf=pass (imf07.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1786467152; b=nA3bIp0cSqfMPwKKV+SOhNP4if1uHoR3Zljtkaswz+IcQ2HUlpFGDVs5Y6jxxoQVLXkj+K i99LUmq/R4/hPFx4ZaJ6wnJe5alMcOulj9xt8ysE7xvXRmBUlhMYVSpNfO0ma2+xpXWcMX M7LCfiZWEUHXPRVLTgaiyvxml8fimY4= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=Jvgo3kgj; spf=pass (imf07.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 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=1786467152; 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=mAasdSnBH2Brz4u/CC8frp1bw4E9g00TGcYdxzOdfsA=; b=VMzIe2E0IYZkyoJYPvuj2hE9Zgg/9H3Uv2B59TUaFHc7vvyHgHF8bm1suF5EPi/wWJgGwq gUC4/AVkjyz7SJIXB4TJWKj7j0duklAF9zoXJaobbpUClHJArz4+FFcwgN+EDXqL6Ufn0Z dMhyW9kRk7HpRwjcIsXxuRBDyPry/hc= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 15E81600AF; Tue, 11 Aug 2026 16:52:32 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 439D81F000E9; Tue, 11 Aug 2026 16:52:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786467151; bh=mAasdSnBH2Brz4u/CC8frp1bw4E9g00TGcYdxzOdfsA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Jvgo3kgjY22ALPkIQ10MF9H8O7gsSZFQkE5mIk5zgk+cuUdPf/TwHKsAj380JXuL9 ZJdMXN32JXVeLsOT0zIz9b12l8r78MZdt5F/tur4FrcUEjjg8eJVMI+gJ2YdDcMhJX XJx8LKunvZ3X84G3aqdNdoLAwld1AfwKkD06m/1UzCgr+HDS9N99IbFU0wyXdpX2Ah xRNi9aUI/Z36g+5E5erW4QK25QCCx85ilTwSlJrawqpXWRvtE4/xoHTTOcU6p2Q1cw 9iXdpTA2g6Ve4dAwca/wQKOSuk04hk53wIbcp/78Vuj9M8ZMNAm8QSRwxmcf6nf/cN WfAjn2fsV2CKQ== Message-ID: Date: Tue, 11 Aug 2026 18:52:06 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 14/20] mm/rmap: use anon pgoff to track MAP_PRIVATE file-backed anon folios To: "Lorenzo Stoakes (ARM)" , Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , "Matthew Wilcox (Oracle)" , Jan Kara , Miaohe Lin , Naoya Horiguchi , Rik van Riel , Harry Yoo , Lance Yang , Kees Cook , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Usama Arif , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Peter Xu , Xu Xin , Chengming Zhou , Arnd Bergmann , Greg Kroah-Hartman , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Sven Schnelle , Alex Deucher , =?UTF-8?Q?Christian_K=C3=B6nig?= , David Airlie , Simona Vetter , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Boris Brezillon , Steven Price , Liviu Dudau , Huang Rui , Matthew Auld , =?UTF-8?Q?Thomas_Hellstr=C3=B6m?= , Rodrigo Vivi , Masami Hiramatsu , Oleg Nesterov , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , James Clark , Jason Gunthorpe , John Hubbard , Muchun Song , Oscar Salvador , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , Youngjun Park Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, kvm@vger.kernel.org, linux-s390@vger.kernel.org, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, intel-xe@lists.freedesktop.org, linux-perf-users@vger.kernel.org, linux-trace-kernel@vger.kernel.org References: <20260806-b4-scalable-cow-virt-pgoff-v4-0-ab318a350404@kernel.org> <20260806-b4-scalable-cow-virt-pgoff-v4-14-ab318a350404@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 805114000C X-Rspam-User: X-Stat-Signature: yc38q7nj5ywq6b3zmmrojywhcxchaio1 X-Rspamd-Server: rspam06 X-HE-Tag: 1786467152-671126 X-HE-Meta: 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 jzaGCQ6t QjeYNxfKtkgwk8ZtKywmDOPTp1Me44ujcnRG7ZsJ0PvXexDU6KrPXA5mPU+cFK78W/9gzz6cAnFRWqCr4l8e2R4YZAZ54AE/0ToX2djQUdkzR7WFzkSp6PSqVsbjc2KtWwHZbKxl9D73HUlwuZ+6AIaQiZSEkgEwWsCcD8syFvx8PohDPXEEfhHFkSQhL98vSXwgy1UfQ1R0xGSgArOfb2DvxrHvS0sPgGMMrYQ1N/34oq9eNwIboNfu30U494BbWDLYWv5LefjmoggObvdSOSFOUtKioydgaHe7Q4bXCDgDmehkn3S95byXktQkxKZ8HVudgK/btZ1t0Ds6cNEEBOVve1Fpd3Na6I8PlZxvmy7NN7QA4E3o9ASYHlu18fhk+Etb8D1XR57TeKfVLT0EsObYaZQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/6/26 22:21, Lorenzo Stoakes (ARM) wrote: > Currently anonymous folios belonging to CoW'd MAP_PRIVATE file-backed > mappings are indexed by their page offset within the file in which they > were originally mapped. > > This differs from anonymous folios belonging to pure anon mappings which > are indexed by their anonymous page offset (the address at which they'd > belong in the VMA when first faulted). > > This change fixes this inconsistency, always indexing anonymous folios by > their anonymous page offset regardless of the VMA to which they belong. > > The foundations have been laid such that we need only switch this > functionality on such by: > > * Using linear_anon_page_index() in __folio_set_anon() to assign the > folio's index to the anonymous linear index rather than the file-backed > one. > > * Otherwise using linear_anon_page_index() in all instances where > anonymous folios are being referenced or manipulated. > > * Replacing vma_address() with vma_filebacked_address() or > vma_anon_address() as appropriate. > > * Updating the merging logic to check that anonymous page offsets are > aligned as well as filebacked ones for MAP_PRIVATE file-backed VMAs, > introducing needs_adjacent_anon_pgoff() to figure out when this is > required. > > * Updating linear_folio_page_index() to invoke linear_anon_page_index() > if the folio is anonymous. > > * Updating vma_address_end() to use the VMA's anonymous page offset when > pvmw->pgoff is anonymous. > > * Correcting folio_within_range() to use anonymous page offset for > anonymous folios. > > This will have no impact on merging of anonymous VMAs, whose page offset > and anonymous page offset are identical, nor will it impact shared > file-backed VMAs, which will continue to be merged based on the file-backed > page offset. > > However, MAP_PRIVATE file-backed mappings must now be aligned on anonymous > page offset as well. > > In most instances this should have no impact on merging of file-backed > mappings, which are usually not merged all that often, let alone > MAP_PRIVATE mapped ones, and rarely remapped and faulted before being moved > back in place (the case in which a merge may now fail). > > One subtle impact of this change is in NUMA interleaving - since commit > 88c91dc58582 ("mempolicy: migration attempt to match interleave nodes"), > migration heuristically tries to maintain interleaving behaviour matching > the policy using folio indices. > > When doing migration of CoW'd MAP_PRIVATE-file backed ranges, the 'base' > upon which the interleaving behaviour is performed will vary for these > ranges. However the commit notes that ranges spanning multiple VMAs will > already cause varying bases, and that this is an acceptable approximation. > > It is very unlikely real world use-cases will be impacted by > this (MAP_PRIVATE file-backed mappings are already an edge case), and all > that will happen is that such ranges will cause interleaving to be rotated > over the CoW'd range, with little to no impact. > > This commit lays the foundations for future scalable CoW work which needs > to track some remaps, meaning that most remap tracking can be avoided, and > in nearly all cases the anonymous page offset will be able to be used to > quickly find the VMA in an mm. > > Note that the need_rmap_locks check doesn't need to be updated, as any > remapping will offset both the anonymous and file-backed page offset, so it > suffices to check only one. > > Signed-off-by: Lorenzo Stoakes (ARM) > --- Acked-by: David Hildenbrand (Arm) -- Cheers, David