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 gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 24517CA0EEB for ; Tue, 19 Aug 2025 11:33:47 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 8F5D210E5B5; Tue, 19 Aug 2025 11:33:46 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=intel.com header.i=@intel.com header.b="SACIUkTb"; dkim-atps=neutral Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.12]) by gabe.freedesktop.org (Postfix) with ESMTPS id B3D8C10E5B5; Tue, 19 Aug 2025 11:33:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1755603225; x=1787139225; h=message-id:subject:from:to:cc:date:in-reply-to: references:content-transfer-encoding:mime-version; bh=CIH7yJkvh3/ZYJwCY/qi2Mlqf8m99Z7mxVV0RImGheY=; b=SACIUkTbkhkqEr10uxmyfLeR9TfOj88ZlnvQOhkNSQdPWaaH22CLoYKG s5fqtMpaeEhGb87dU9PXzxbfROLsYRfRT9dlC9YR/0kaUO82vky0/FocW oPHVTcOiUoaomBSCnJKFYsaK246Dk+El7rjAeIn7duGYbAmkkhUqsCOfI nrw20TEU5WFtE8BQzpHS2yCmBCMBuq53GX8ZLsaaJuijmBqJAxHK6P6Jr hcS++Rjk/WtXYMewzNONDsfQpKav2MgakkrMX7MJcBJ3H7Vy7WAs3ml+z VutMkmAw+WB+UWtP7NRW5JBnsrlefLruH/kpSPKsFlZAfH5+l89AuEm8R A==; X-CSE-ConnectionGUID: 1YkeDz1SQXK82LXzyLP1hQ== X-CSE-MsgGUID: WC+zs9XZRsuiDFvA3JFnnA== X-IronPort-AV: E=McAfee;i="6800,10657,11526"; a="61653783" X-IronPort-AV: E=Sophos;i="6.17,300,1747724400"; d="scan'208";a="61653783" Received: from fmviesa002.fm.intel.com ([10.60.135.142]) by fmvoesa106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Aug 2025 04:33:45 -0700 X-CSE-ConnectionGUID: 9h5gT3AbRN+Hotu/iwO0Rw== X-CSE-MsgGUID: pw3f4t59THSX7xndiXJpeg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.17,300,1747724400"; d="scan'208";a="191520115" Received: from ncintean-mobl1.ger.corp.intel.com (HELO [10.245.244.175]) ([10.245.244.175]) by fmviesa002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Aug 2025 04:33:43 -0700 Message-ID: Subject: Re: [RFC PATCH 1/6] mm/mmu_notifier: Allow multiple struct mmu_interval_notifier passes From: Thomas =?ISO-8859-1?Q?Hellstr=F6m?= To: Alistair Popple , Jason Gunthorpe Cc: Matthew Brost , intel-xe@lists.freedesktop.org, Andrew Morton , Simona Vetter , Dave Airlie , dri-devel@lists.freedesktop.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Christian =?ISO-8859-1?Q?K=F6nig?= Date: Tue, 19 Aug 2025 13:33:40 +0200 In-Reply-To: <4lsv2lcd7lssyvcjvkqe4t2foubxbhuxrt2ptzee3csymz5gg3@jwrg3xow72lm> References: <20250809135137.259427-1-thomas.hellstrom@linux.intel.com> <20250809135137.259427-2-thomas.hellstrom@linux.intel.com> <20250818160726.GH599331@ziepe.ca> <20250818163617.GI599331@ziepe.ca> <20250818164655.GJ599331@ziepe.ca> <4lsv2lcd7lssyvcjvkqe4t2foubxbhuxrt2ptzee3csymz5gg3@jwrg3xow72lm> Organization: Intel Sweden AB, Registration Number: 556189-6027 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.54.3 (3.54.3-1.fc41) MIME-Version: 1.0 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Tue, 2025-08-19 at 19:55 +1000, Alistair Popple wrote: > On Mon, Aug 18, 2025 at 01:46:55PM -0300, Jason Gunthorpe wrote: > > On Mon, Aug 18, 2025 at 09:44:01AM -0700, Matthew Brost wrote: > > > On Mon, Aug 18, 2025 at 01:36:17PM -0300, Jason Gunthorpe wrote: > > > > On Mon, Aug 18, 2025 at 09:25:20AM -0700, Matthew Brost wrote: > > > > > I think this choice makes sense: it allows embedding the wait > > > > > state from > > > > > the initial notifier call into the pass structure. Patch [6] > > > > > shows this > > > > > by attaching the issued TLB invalidation fences to the pass. > > > > > Since a > > > > > single notifier may be invoked multiple times with different > > > > > ranges but > > > > > the same seqno, > > > >=20 > > > > That should be explained, but also seems to be a bit of a > > > > different > > > > issue.. > > > >=20 > > > > If the design is really to only have two passes and this linked > > > > list > > > > is about retaining state then there should not be so much > > > > freedom to > > > > have more passes. > > >=20 > > > I=E2=80=99ll let Thomas weigh in on whether we really need more than = two > > > passes; > > > my feeling is that two passes are likely sufficient. It=E2=80=99s als= o > > > worth > > > noting that the linked list has an added benefit: the notifier > > > tree only > > > needs to be walked once (a small time-complexity win). > >=20 > > You may end up keeping the linked list just with no way to add a > > third > > pass. >=20 > It seems to me though that linked list still adds unnecessary > complexity. I > think this would all be much easier to follow if we just added two > new callbacks > - invalidate_start() and invalidate_end() say. One thing that the linked list avoids, though, is traversing the interval tree two times. It has O(n*log(n)) whereas the linked list overhead is just O(n_2pass). >=20 > Admitedly that would still require the linked list (or something > similar) to > retain the ability to hold/pass a context between the start and end > callbacks. > Which is bit annoying, it's a pity we need to allocate memory in a > performance > sensitive path to effectively pass (at least in this case) a single > pointer. I > can't think of any obvious solutions to that though. One idea is for any two-pass notifier implementation to use a small pool. That would also to some extent mitigate the risk of out-of-memory with GFP_NOWAIT. /Thomas >=20 > > Jason > >=20