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 E87C9C61DBE for ; Sat, 29 Aug 2026 11:00:21 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id C20FA6B008C; Sat, 29 Aug 2026 07:00:20 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id BD2596B0092; Sat, 29 Aug 2026 07:00:20 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id AE7B86B0095; Sat, 29 Aug 2026 07:00:20 -0400 (EDT) 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 8EF196B008C for ; Sat, 29 Aug 2026 07:00:20 -0400 (EDT) Received: from smtpin29.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 23866C0691 for ; Sat, 29 Aug 2026 11:00:20 +0000 (UTC) X-FDA: 85154013000.29.BF1C5E0 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf18.hostedemail.com (Postfix) with ESMTP id 6CE091C000C for ; Sat, 29 Aug 2026 11:00:18 +0000 (UTC) Authentication-Results: imf18.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=FuX452UX; spf=pass (imf18.hostedemail.com: domain of rppt@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=rppt@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=1788001218; 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=gXc6uvmEEbs0tjpDmzTEGwxIlYg9TWDsfiwiPxngOzE=; b=cMd+gNTgvQIzTWn8WkHzZ4VXU8EkExXEakQU8EaWIsNe95x67xIvINCXksxqhhd1EnK1MA AMjSbwThLW3QLZx3E7zizGRK2N2D8snDHkh0oQGa1K40SZuPU17uIRSVuZ0GNK/Ftx4Upa CM0+ERWlt6ogqK34CAhU8bfcY9ZQKOQ= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1788001218; b=2t5mwyPBEX9SUnzphibKufnthypV0uydAZVnM0iT9B7btW0Y6GkIg6OQS4UuTF8+S2tD9X UajYV5E+oekUBkP7rrrdtk3unscbG361/P7YUUd52HwHEKQe4vMr0VSCCKg+rk0Iz1CONE kaVFCKyqrRMhMmrZjqhGUGvXCEhm7Tk= ARC-Authentication-Results: i=1; imf18.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=FuX452UX; spf=pass (imf18.hostedemail.com: domain of rppt@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=rppt@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 35CF241600; Sat, 29 Aug 2026 11:00:17 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9ACDE1F000E9; Sat, 29 Aug 2026 11:00:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788001217; bh=gXc6uvmEEbs0tjpDmzTEGwxIlYg9TWDsfiwiPxngOzE=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=FuX452UXi8Md7T20vL745dUi69Ui1QV/KOxLJj/ty2S9fwWxlS38Y55KfLpQWahhr hopl168pK0jYYEkNMg236NXMW6s3gtPGn3OvYa4cKJiZ3YyALIKdJwqiSbyfy7rnrL PXnGZl2bYgkAb+OsTZMJfjlYbazbGpwXeglNtUEFeqIgSiw59ymCfL5oNAX0RsVmLf T2vqLfykJ4tJGrDwUQkkVsFB69QnkEz41lElPHW4pzsVHGhlXtNPu50Q2Esmi3tJng O38SgqKGHA2jitUBjxGfntIUAYcJMU8BeA3MtqD6nWhNjIAqTUVLfyVtTFW8ciUo3x Kn6KLeUl0ZKlQ== Date: Sat, 29 Aug 2026 14:00:03 +0300 From: Mike Rapoport To: "David Hildenbrand (Arm)" Cc: "Lorenzo Stoakes (ARM)" , Andrew Morton , Baolin Wang , Barry Song , Dev Jain , Hugh Dickins , Jann Horn , Jason Gunthorpe , John Hubbard , Jonathan Corbet , Lance Yang , "Liam R. Howlett" , Masami Hiramatsu , Mathieu Desnoyers , Michal Hocko , Muchun Song , Nico Pache , Oscar Salvador , Pedro Falcato , Peter Xu , Ryan Roberts , Shakeel Butt , Shuah Khan , Steven Rostedt , Suren Baghdasaryan , Usama Arif , Vlastimil Babka , Zi Yan , linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH 6/6] userfaultfd: collapse VM_UFFD_{MISSING,WP,MINOR,RWP} into single VM_UFFD Message-ID: References: <20260823-uffd-vm-flags-v1-v1-0-3086981b33cf@kernel.org> <20260823-uffd-vm-flags-v1-v1-6-3086981b33cf@kernel.org> <37f6af95-950e-4457-886e-6548d4719f0d@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <37f6af95-950e-4457-886e-6548d4719f0d@kernel.org> X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 6CE091C000C X-Stat-Signature: durzymgd6ee53xdxg6bt1yr8g8iqtxgk X-HE-Tag: 1788001218-532816 X-HE-Meta: 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 gD41ZpZo SKX3TseIU+glee1ID5iHIKKa7+/OVza1y7/w1MyfglAanUoTuZmDPgfqiQjcCL6Avis/xh8PbRWcRooZuCW08eBR9N8xcSmp1BGKopnDK1OmpVhB3Kwu39QL58x7OZvh/Wt/THfAsiMz944dlTNcJgZfMOV2Kjuuhrl3YjeXBNsvhbNmdFBEJLTAp5rA9T6t5u8LKo2vC8pqRo5SsGFnQKvaLUEYlb+Du5BhrfNbXo6ddiI5WbyYW1AyRSTB7TNvAIX78ZsqrJ6bU/+N/YuzpJ39hY09k76+OlUpVp/aM9yw8tEKr4P/9zwYwYQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Aug 27, 2026 at 05:19:30PM +0200, David Hildenbrand (Arm) wrote: > On 8/27/26 13:18, Lorenzo Stoakes (ARM) wrote: > > On Thu, Aug 27, 2026 at 12:16:32PM +0100, Lorenzo Stoakes (ARM) wrote: > >> So actually you're increasing by a cacheline and increasing the VMA size by > >> 64 bytes, i.e. 1/3, which is unacceptable obviously. > >> > >> Maybe there's something that can be done with: > >> > >> /* forced alignments: 1 */ > >> > >> Perhaps? But that looks potentially ugly. > >> > > > > I say elsewhere (or think I do) but to highlight - I think probably we could fix > > this by putting the flags in the low bits of vm_uffd_state.ctx? > > if that's possible that would be clearly preferable memory-wise. This gives only 4 bits and makes this completely not extendable. So I think I'll drop this for now and wait until VMA grows another cache line or until having per-VMA uffd state rather than a pointer to per-fd context is a must. > -- > Cheers, > > David -- Sincerely yours, Mike.