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=-2.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,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 0AF6BC32750 for ; Fri, 2 Aug 2019 14:24:46 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 D27BE20679 for ; Fri, 2 Aug 2019 14:24:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="M2IKymwS" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D27BE20679 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=6vUVuCH88Cq/cjKl7bUtAZnLRndW/CiNnyj4x7rUnT0=; b=M2IKymwS7a20d2 hAr3UlFmL4wqTLuwCIOlNYoX6aOfLLG+ewt8Q7W09q65SmKEoDJ6N4JhCj+3CeYqMtaLhOalU0jlz 05L1Ix32s55nJORcj/7h65VcZ3ImOAXJ7f1WZ0auDOW2YKGCjsNz34+0tpugVsEBfTKQy5bAb1Cmk Sn05XxE9GpQkzY2hrnh+at9zMgdk9VtizY7wOgGKaY7ZebUDUoZTs171NCRvGSrWg1FHI0dwH46kl /XNjFsSw5FdOM6GwrfAUQM53ZI9izEz7MkB0RcHCs+AEJCLhvibjxxQ52UvChmHDZUKNw6FzWeOS6 a1a7E5zRoVCqclHVhlzg==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1htYU9-0007Lv-Ib; Fri, 02 Aug 2019 14:24:45 +0000 Received: from willy by bombadil.infradead.org with local (Exim 4.92 #3 (Red Hat Linux)) id 1htYU7-0007La-VU; Fri, 02 Aug 2019 14:24:43 +0000 Date: Fri, 2 Aug 2019 07:24:43 -0700 From: Matthew Wilcox To: Jan Kara Subject: Re: [PATCH 00/34] put_user_pages(): miscellaneous call sites Message-ID: <20190802142443.GB5597@bombadil.infradead.org> References: <20190802022005.5117-1-jhubbard@nvidia.com> <20190802091244.GD6461@dhcp22.suse.cz> <20190802124146.GL25064@quack2.suse.cz> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190802124146.GL25064@quack2.suse.cz> User-Agent: Mutt/1.11.4 (2019-03-13) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-fbdev@vger.kernel.org, kvm@vger.kernel.org, Dave Hansen , Dave Chinner , dri-devel@lists.freedesktop.org, Michal Hocko , linux-mm@kvack.org, sparclinux@vger.kernel.org, Ira Weiny , Dan Williams , devel@driverdev.osuosl.org, rds-devel@oss.oracle.com, linux-rdma@vger.kernel.org, x86@kernel.org, amd-gfx@lists.freedesktop.org, Christoph Hellwig , Jason Gunthorpe , xen-devel@lists.xenproject.org, devel@lists.orangefs.org, linux-media@vger.kernel.org, John Hubbard , intel-gfx@lists.freedesktop.org, john.hubbard@gmail.com, linux-block@vger.kernel.org, =?iso-8859-1?B?Suly9G1l?= Glisse , linux-rpi-kernel@lists.infradead.org, ceph-devel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-nfs@vger.kernel.org, netdev@vger.kernel.org, LKML , linux-xfs@vger.kernel.org, linux-crypto@vger.kernel.org, linux-fsdevel@vger.kernel.org, Andrew Morton Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Aug 02, 2019 at 02:41:46PM +0200, Jan Kara wrote: > On Fri 02-08-19 11:12:44, Michal Hocko wrote: > > On Thu 01-08-19 19:19:31, john.hubbard@gmail.com wrote: > > [...] > > > 2) Convert all of the call sites for get_user_pages*(), to > > > invoke put_user_page*(), instead of put_page(). This involves dozens of > > > call sites, and will take some time. > > > > How do we make sure this is the case and it will remain the case in the > > future? There must be some automagic to enforce/check that. It is simply > > not manageable to do it every now and then because then 3) will simply > > be never safe. > > > > Have you considered coccinele or some other scripted way to do the > > transition? I have no idea how to deal with future changes that would > > break the balance though. > > Yeah, that's why I've been suggesting at LSF/MM that we may need to create > a gup wrapper - say vaddr_pin_pages() - and track which sites dropping > references got converted by using this wrapper instead of gup. The > counterpart would then be more logically named as unpin_page() or whatever > instead of put_user_page(). Sure this is not completely foolproof (you can > create new callsite using vaddr_pin_pages() and then just drop refs using > put_page()) but I suppose it would be a high enough barrier for missed > conversions... Thoughts? I think the API we really need is get_user_bvec() / put_user_bvec(), and I know Christoph has been putting some work into that. That avoids doing refcount operations on hundreds of pages if the page in question is a huge page. Once people are switched over to that, they won't be tempted to manually call put_page() on the individual constituent pages of a bvec. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel