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 76F7FC55179 for ; Mon, 3 Aug 2026 13:22:55 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 6164D6B00AC; Mon, 3 Aug 2026 09:22:54 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5ED886B00AD; Mon, 3 Aug 2026 09:22:54 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5041F6B00AE; Mon, 3 Aug 2026 09:22:54 -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 3119C6B00AC for ; Mon, 3 Aug 2026 09:22:54 -0400 (EDT) Received: from smtpin12.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 605D64065D for ; Mon, 3 Aug 2026 09:47:02 +0000 (UTC) X-FDA: 85059479484.12.DF6C064 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf23.hostedemail.com (Postfix) with ESMTP id 9FEA114000B for ; Mon, 3 Aug 2026 09:47:00 +0000 (UTC) Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=ZWQLDfqW; spf=pass (imf23.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=1785750420; 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=WmTYhKzT9eCB53aTI2koOjOPsk0BfddrSlJB+6MBGwY=; b=MrHgv91AttWD6Txquk8bBJ1dSIj4yFP1cU6+sHGPNgfjgwZcmUM1iojZpmR6pE3BHw/yYs aeQ7Bo3HbX0YmKul6+n0xcNJ7Ud77fLuoZ/4UhrwIqdiS0HxpIHHRC/7AFD10pBQMPcJkq Qtr2locPFILqRDZtZ6INY0uGhx3nnb8= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1785750420; b=4V9dkGqH6Qt6toxoDz4lGIwINnBPGRQieztpQ1brAr9UKmKe6D8yJ+OwA3MrThfRgkdfgC DoghBUo+5UOsv2As53NazmNmZflAGIJOeRNthWGwv2my+iAy/ZqlH5bohHMyds0iC0vXIB 4awTOUzmhscU/tbbA8nytPtBPNTl3J0= ARC-Authentication-Results: i=1; imf23.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=ZWQLDfqW; spf=pass (imf23.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 C2D6B42B39; Mon, 3 Aug 2026 09:46:59 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0CE051F00A3A; Mon, 3 Aug 2026 09:46:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785750419; bh=WmTYhKzT9eCB53aTI2koOjOPsk0BfddrSlJB+6MBGwY=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=ZWQLDfqWcbka5ukiKfEue5Pje/KLYTUCEL5GxPuZMk668y5yZrrbvVfbFJWP7zA3e oBjiNDQIR20BZMymwsL8s8U4CgxsV2V+oT+C9EgnHDcjtE+SwZEE6vBUCocLBJvZAZ oS+OEr9lXrBDD416GfBtp+MCtpmUD8iIXcgzxEGAY37TuPudeHosUsXFDYJPtxheE2 cw42f7Cw+SZy7rm1DqhT7aJnyu7AT/KbfLNaDDrmKc4eFfi2oLMcOLG7Cqu8lnj76k 5LXlFPVySlsRPcciVBCN9LU0GKcoCT/+RFL04RwAtqQuRDE062VqX1KBz7K37udTlr LgPcrK9j40tWQ== Date: Mon, 3 Aug 2026 10:46:35 +0100 From: "Lorenzo Stoakes (ARM)" To: "David Hildenbrand (Arm)" Cc: 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 , 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> <2ac2746f-18b4-4960-8628-82e87c2140ce@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2ac2746f-18b4-4960-8628-82e87c2140ce@kernel.org> X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 9FEA114000B X-Stat-Signature: w3oehbhwn9di7qmjco4q9ng1st4mngor X-Rspam-User: X-HE-Tag: 1785750420-838092 X-HE-Meta: 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 Jug9OOuW 6qz0sziz4cR9nQ2TLgUaeblTu8nPQSJVmpEhFEYhXEMMyj7CkiFX6toL7Abof1RMtiA3Zgvzpd6Viln0+dbG9UxjzO6Nbsps9YX7jSBFLLniZaSC/ci9MZqgAJoBhprxVXvZ+ae6PBNzbymTYfFrJoLKLiV+nL+yrHsxONIG7fgWqzsenaFnSD+AtYHM4Xb5TtRxCENgBjd7ufVRrypl4bxmfR4Wtwf6OSgB/LEOb9Gm/du1/QRaED+L1PkGGW9sOShqQkX6PlgXq8zW3agc5KibH70SRkE368ieU0iLHWWmebUXRbUpgdSi+I7eiM6PYLU1GsNFWDUhe/wZ8PeW3c+9c61tqnDyOUEqw Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Aug 03, 2026 at 11:28:28AM +0200, David Hildenbrand (Arm) wrote: > On 7/29/26 18:48, Lorenzo Stoakes (ARM) wrote: > > This patch establishes fields within the vm_area_struct type to store the > > anonymous page offset of VMAs. > > Nit: Avoid "This patch". Just say "Establish ..." (I was surprised to find > that even Documentation/process/submitting-patches.rst document this) Yeah ever since Boris nagged me I've (possibly reluctantly? :P) found that using the active voice is a lot clearer and have been using that more so. Will fix up on respin. > > > > > 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) > > --- > > [...] > > > +static inline void __vma_set_anon_pgoff(struct vm_area_struct *vma, pgoff_t pgoff) > > +{ > > +#ifdef CONFIG_64BIT > > + vma->__vm_anon_pgoff_hi = pgoff >> 32; > > +#endif > > + vma->__vm_anon_pgoff_lo = pgoff & GENMASK(31, 0); > > +} > > + > > +static inline void vma_set_anon_pgoff(struct vm_area_struct *vma, pgoff_t pgoff) > > +{ > > + vma_assert_can_modify(vma); > > + __vma_set_anon_pgoff(vma, pgoff); > > +} > > + > > static inline void vma_add_pgoff(struct vm_area_struct *vma, pgoff_t delta) > > { > > vma_assert_can_modify(vma); > > diff --git a/mm/vma_init.c b/mm/vma_init.c > > index 715feee283f0..baa7e82f47e3 100644 > > --- a/mm/vma_init.c > > +++ b/mm/vma_init.c > > @@ -51,6 +51,7 @@ static void vm_area_init_from(const struct vm_area_struct *src, > > dest->vm_end = src->vm_end; > > dest->anon_vma = src->anon_vma; > > dest->vm_pgoff = vma_start_pgoff(src); > > + __vma_set_anon_pgoff(dest, vma_start_anon_pgoff(src)); > > It would be cleaner if both interfaces would either contain "start" or not contain it. > > The former would be better > > __vma_set_start_anon_pgoff(dest, vma_start_anon_pgoff(src)); Ack that's fair, will update it. > > Acked-by: David Hildenbrand (Arm) Thanks! > > -- > Cheers, > > David -- Cheers, Lorenzo