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 88F5BC53200 for ; Wed, 29 Jul 2026 17:12:23 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 344546B008A; Wed, 29 Jul 2026 13:12:22 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 31B4A6B008C; Wed, 29 Jul 2026 13:12:22 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 230A06B0092; Wed, 29 Jul 2026 13:12:22 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 04C396B008A for ; Wed, 29 Jul 2026 13:12:21 -0400 (EDT) Received: from smtpin19.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 83B491A0710 for ; Wed, 29 Jul 2026 17:12:21 +0000 (UTC) X-FDA: 85042457682.19.164D795 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf05.hostedemail.com (Postfix) with ESMTP id BB89A100012 for ; Wed, 29 Jul 2026 17:12:19 +0000 (UTC) Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=Arj5dKsi; spf=pass (imf05.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@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=1785345139; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=ydzhtkpxp5BQwBhGox1Nkoqh6PfrK9kxbIuBs5y9N6A=; b=vFR/8JCqJRSMFFu9D2LO3U5cv0luNrVK3yBWAMnhC4eRSWY9Rzv8N4kT+6KSd451w800yR i6FuEzNOMhlgyb3BxrrrD/vOLNco7QqlACCLuCTxo4k5LRLGjzxx+I5tmuEm643E2neyIq Nw3j7LLCfYaRsWaZFViYuG5+yOfC3QQ= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1785345139; b=fglPp2kYY6bQOGFsxv60aIRCbdJYshqEokH6QY5WUhOMKtxx7V3ES9XsX0uYA9VXsg5E+G hUVEaMOooiuI4JCWt0yTzDghFwN2h9QA/il5ioDbMX7ZXO7eIyYQ9owQrI4MYCmmPtLunK 9Sa1CwgSo2FHumHiM2MdwGr/atQkfwg= ARC-Authentication-Results: i=1; imf05.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=Arj5dKsi; spf=pass (imf05.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 9195642A46; Wed, 29 Jul 2026 17:12:18 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E102D1F000E9; Wed, 29 Jul 2026 17:12:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785345138; bh=ydzhtkpxp5BQwBhGox1Nkoqh6PfrK9kxbIuBs5y9N6A=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=Arj5dKsiADp8nzEpUb2nTNNXinho7z4KB+KTxpgxU3M3yvn60+RFOmnNHG5ecfqAJ UQ5o7ZZJ1dBuhIe5OQAvmNXX804KdLEqbcExYpeFPsKkoliynK1brjrpy8v8wuVNAj 9tsdNB9T1AJ3pPoagVRqpo6EY7IIkwOzio0o/hV19or7vSRjVCruI+SX9wHjpCpWnq 3EVAHecRj4333tJh3roqqmzcBe0I4jHe1JIFXeEFLRONNo0TQ602dozpVVFamqGigb v9VRmlJMbiQHnQnkwOZdOjZN+AHhn5XH/rHEPDgAnTOiyDBTaFAU4M18N0KZlIcwPZ qX4IkiEsH6+6w== Date: Wed, 29 Jul 2026 18:11:56 +0100 From: "Lorenzo Stoakes (ARM)" To: Andrew Morton , David Hildenbrand , "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 Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH v3 01/15] mm/vma: introduce VMA anon page offset field and add helpers Message-ID: References: <20260729-b4-scalable-cow-virt-pgoff-v3-0-e8ecfefea812@kernel.org> <20260729-b4-scalable-cow-virt-pgoff-v3-1-e8ecfefea812@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260729-b4-scalable-cow-virt-pgoff-v3-1-e8ecfefea812@kernel.org> X-Rspamd-Queue-Id: BB89A100012 X-Stat-Signature: n3m5ykbpk9ejkz7hmojh44ubd3yx93bj X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1785345139-920391 X-HE-Meta: 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 rJuhL77x An2PCUcF1VCiD7k7Fqut7nvOVc2xXjkAMuIxX+esn0Pukb3wkBBgjyZDjBsSEMVphU7sfsaamfcjw9UOpQIi5KmGtEwgKFfFElUBMbODTgWv9m1/waUaVBnS17IO3CHc7fni6B8BoUnbL8DO2nJfK+zrWsV9lX9lpw60ovY7kJk5VK+liShkn54R8MUgF+oCPZCWewuo28EwZCuQkzTRthdzMxoqkRZLodn5c1beXf9d6+Wwa+4v5fzoGJL9LpmbTKCULxhVbsrPVAfA9UwN2xl6euomDcRLaKYM05WkUHvoh5eQUwuPoupq31OZTGBgAg+t7QHFegGDm5JZx93sKRnUWwu/NJ4mBmdHgzd4Q6D6xjzPUAmouWjVgsEeviY2OmOHwdydof2axWo87wU87rrHIClJtM+R5hx+N Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Jul 29, 2026 at 05:48:36PM +0100, Lorenzo Stoakes (ARM) wrote: > This patch establishes fields within the vm_area_struct type to store the > anonymous page offset of VMAs. > > The anonymous page offset of a VMA is equal to vma->vm_start >> PAGE_SHIFT > if they are unfaulted or were not remapped, otherwise it is equal to this > value at the point of first fault. > > Currently, anonymous folios belonging to CoW'd MAP_PRIVATE-mapped > file-backed VMAs are tracked by their file offset. By adding anonymous > offset as a property of VMAs, we can now track them by their anonymous page > offset instead. > > By tracking this, we provide the means by which to eliminate this > inconsistency, and more importantly lay the foundations for future work for > the scalable CoW anonymous rmap rework. > > This patch simply adds the fields and some simple helpers. Subsequent > patches will update mm code to make use of these fields correctly. > > The fields chosen are packed in the VMA such that, for 64-bit kernel > builds, no additional space is taken up. > > The first field is present on cacheline 0 containing key VMA fields, and > the second on cacheline 3, which contains file-backed reverse mapping > fields. > > Given the relative time spent accessing reverse mapping fields as well as > updating them, there shouldn't be any performance impact here from false > sharing. > > Update the VMA userland tests to account for this change. > > No callsites are updated yet, so no functional change intended. > > Signed-off-by: Lorenzo Stoakes (ARM) Sorry I forgot to run b4 trailers -u :) Andrew please add Xu's tag (thanks Xu!): Reviewed-by: Xu Xin Cheers, Lorenzo