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 5EEC9C4338F for ; Fri, 20 Aug 2021 05:05:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2902060E78 for ; Fri, 20 Aug 2021 05:05:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231148AbhHTFFq (ORCPT ); Fri, 20 Aug 2021 01:05:46 -0400 Received: from verein.lst.de ([213.95.11.211]:39719 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229457AbhHTFFq (ORCPT ); Fri, 20 Aug 2021 01:05:46 -0400 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) Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org 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.