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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 2A7A1C33CB1 for ; Wed, 15 Jan 2020 15:23:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EDA1D24679 for ; Wed, 15 Jan 2020 15:23:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="hhbgi8BJ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726248AbgAOPXh (ORCPT ); Wed, 15 Jan 2020 10:23:37 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:48766 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726165AbgAOPXh (ORCPT ); Wed, 15 Jan 2020 10:23:37 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Transfer-Encoding :Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=XJx25SjGDNaPjSZ5TNemDMINDpbBYIW/xJOLgTsR2QM=; b=hhbgi8BJKTkNcGbj/zsunWm8Nk 5/QjY8sMr0mKKH9pQML6hCHgjupQSuiVpFa35irs5bk6Fyb0UXZ1Yk33/ewO5HcNonK3bLaNQlK9j vKW8gUSqaVd9vEKlh6jNUdhGn+SVvs43+luv2lVS3kKMoCNgeVxJWJGs0m9STdgU4Qtt71bfJRfCg Hs7bX3HZshLtu6+z7ViFzZPM/Q11Zm0+3LL1wi1u6yCjGgTKJxM/vuInUUiL02Q9vr1wQQHktXl01 ud7iaVtdov/flVsEByz9WQ5V6SiyJzpX3YWSsvca9IYSpvPI0fNOHBgvyQHf7/UrLeeWuISjdgkdd igfjbtlQ==; Received: from hch by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1irkVe-0007PR-Hi; Wed, 15 Jan 2020 15:23:06 +0000 Date: Wed, 15 Jan 2020 07:23:06 -0800 From: Christoph Hellwig To: John Hubbard Cc: Andrew Morton , Al Viro , Alex Williamson , Benjamin Herrenschmidt , =?iso-8859-1?Q?Bj=F6rn_T=F6pel?= , Christoph Hellwig , Dan Williams , Daniel Vetter , Dave Chinner , David Airlie , "David S . Miller" , Ira Weiny , Jan Kara , Jason Gunthorpe , Jens Axboe , Jonathan Corbet , =?iso-8859-1?B?Suly9G1l?= Glisse , "Kirill A . Shutemov" , Magnus Karlsson , Mauro Carvalho Chehab , Michael Ellerman , Michal Hocko , Mike Kravetz , Paul Mackerras , Shuah Khan , Vlastimil Babka , bpf@vger.kernel.org, dri-devel@lists.freedesktop.org, kvm@vger.kernel.org, linux-block@vger.kernel.org, linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-media@vger.kernel.org, linux-rdma@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, netdev@vger.kernel.org, linux-mm@kvack.org, LKML , Christoph Hellwig Subject: Re: [PATCH v12 04/22] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages Message-ID: <20200115152306.GA19546@infradead.org> References: <20200107224558.2362728-1-jhubbard@nvidia.com> <20200107224558.2362728-5-jhubbard@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200107224558.2362728-5-jhubbard@nvidia.com> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Tue, Jan 07, 2020 at 02:45:40PM -0800, John Hubbard wrote: > An upcoming patch changes and complicates the refcounting and > especially the "put page" aspects of it. In order to keep > everything clean, refactor the devmap page release routines: > > * Rename put_devmap_managed_page() to page_is_devmap_managed(), > and limit the functionality to "read only": return a bool, > with no side effects. > > * Add a new routine, put_devmap_managed_page(), to handle > decrementing the refcount for ZONE_DEVICE pages. > > * Change callers (just release_pages() and put_page()) to check > page_is_devmap_managed() before calling the new > put_devmap_managed_page() routine. This is a performance > point: put_page() is a hot path, so we need to avoid non- > inline function calls where possible. > > * Rename __put_devmap_managed_page() to free_devmap_managed_page(), > and limit the functionality to unconditionally freeing a devmap > page. > > This is originally based on a separate patch by Ira Weiny, which > applied to an early version of the put_user_page() experiments. > Since then, Jérôme Glisse suggested the refactoring described above. I'm really not sold on this scheme. Note that I think it is particularly bad, but it also doesn't seem any better than what we had before, and it introduced quite a bit more code.