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 X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0AA59C4338F for ; Fri, 20 Aug 2021 13:05:37 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 509B86101A for ; Fri, 20 Aug 2021 13:05:36 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 509B86101A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id A09016EA87; Fri, 20 Aug 2021 13:05:34 +0000 (UTC) Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by gabe.freedesktop.org (Postfix) with ESMTPS id 0DA966E832; Fri, 20 Aug 2021 05:05:09 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id F19846736F; Fri, 20 Aug 2021 07:05:04 +0200 (CEST) Date: Fri, 20 Aug 2021 07:05:04 +0200 From: Christoph Hellwig To: Felix Kuehling Cc: Christoph Hellwig , Alex Sierra , akpm@linux-foundation.org, linux-mm@kvack.org, rcampbell@nvidia.com, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, jgg@nvidia.com, jglisse@redhat.com, Roger Pau Monne , Dan Williams , Boris Ostrovsky Subject: Re: [PATCH v6 08/13] mm: call pgmap->ops->page_free for DEVICE_GENERIC pages Message-ID: <20210820050504.GB27083@lst.de> References: <20210813063150.2938-1-alex.sierra@amd.com> <20210813063150.2938-9-alex.sierra@amd.com> <20210815154047.GC32384@lst.de> <7a55366f-bd65-7ab9-be9e-3bfd3aea3ea1@amd.com> <20210817055031.GC4895@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) X-Mailman-Approved-At: Fri, 20 Aug 2021 13:05:32 +0000 X-BeenThere: amd-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Discussion list for AMD gfx List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: amd-gfx-bounces@lists.freedesktop.org Sender: "amd-gfx" On Tue, Aug 17, 2021 at 11:44:54AM -0400, Felix Kuehling wrote: > >> That's a good catch. Existing drivers shouldn't need a page_free > >> callback if they didn't have one before. That means we need to add a > >> NULL-pointer check in free_device_page. > > Also the other state clearing (__ClearPageWaiters/mem_cgroup_uncharge/ > > ->mapping = NULL). > > > > In many ways this seems like you want to bring back the DEVICE_PUBLIC > > pgmap type that was removed a while ago due to the lack of users > > instead of overloading the generic type. > > I think so. I'm not clear about how DEVICE_PUBLIC differed from what > DEVICE_GENERIC is today. As I understand it, DEVICE_PUBLIC was removed > because it was unused and also known to be broken in some ways. > DEVICE_GENERIC seemed close enough to what we need, other than not being > supported in the migration helpers. > > Would you see benefit in re-introducing DEVICE_PUBLIC as a distinct > memory type from DEVICE_GENERIC? What would be the benefits of making > that distinction? The old DEVICE_PUBLIC mostly different in that it allowed the page to be returned from vm_normal_page, which I think was horribly buggy. But the point is not to bring back these old semantics. The idea is to be able to differeniate between your new coherent on-device memory and the existing DEVICE_GENERIC. That is call the code in free_devmap_managed_page that is currently only used for device private pages also for your new public device pages without affecting the devdax and xen use cases.