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=-2.2 required=3.0 tests=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 C8F9FC3A59C for ; Fri, 16 Aug 2019 15:44:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A554E21721 for ; Fri, 16 Aug 2019 15:44:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727484AbfHPPoG (ORCPT ); Fri, 16 Aug 2019 11:44:06 -0400 Received: from mx2.suse.de ([195.135.220.15]:60226 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727311AbfHPPoG (ORCPT ); Fri, 16 Aug 2019 11:44:06 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id B42A1AD0F; Fri, 16 Aug 2019 15:44:04 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 1D8051E4009; Fri, 16 Aug 2019 17:44:04 +0200 (CEST) Date: Fri, 16 Aug 2019 17:44:04 +0200 From: Jan Kara To: Vlastimil Babka Cc: Jan Kara , John Hubbard , Ira Weiny , Andrew Morton , Christoph Hellwig , Dan Williams , Dave Chinner , Jason Gunthorpe , =?iso-8859-1?B?Suly9G1l?= Glisse , LKML , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-rdma@vger.kernel.org Subject: Re: [RFC PATCH 2/2] mm/gup: introduce vaddr_pin_pages_remote() Message-ID: <20190816154404.GF3041@quack2.suse.cz> References: <38d2ff2f-4a69-e8bd-8f7c-41f1dbd80fae@nvidia.com> <20190813210857.GB12695@iweiny-DESK2.sc.intel.com> <90e5cd11-fb34-6913-351b-a5cc6e24d85d@nvidia.com> <20190814234959.GA463@iweiny-DESK2.sc.intel.com> <2cbdf599-2226-99ae-b4d5-8909a0a1eadf@nvidia.com> <20190815132622.GG14313@quack2.suse.cz> <20190815133510.GA21302@quack2.suse.cz> <0d6797d8-1e04-1ebe-80a7-3d6895fe71b0@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0d6797d8-1e04-1ebe-80a7-3d6895fe71b0@suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 16-08-19 10:47:21, Vlastimil Babka wrote: > On 8/15/19 3:35 PM, Jan Kara wrote: > >> > >> So when the GUP user uses MMU notifiers to stop writing to pages whenever > >> they are writeprotected with page_mkclean(), they don't really need page > >> pin - their access is then fully equivalent to any other mmap userspace > >> access and filesystem knows how to deal with those. I forgot out this case > >> when I wrote the above sentence. > >> > >> So to sum up there are three cases: > >> 1) DIO case - GUP references to pages serving as DIO buffers are needed for > >> relatively short time, no special synchronization with page_mkclean() or > >> munmap() => needs FOLL_PIN > >> 2) RDMA case - GUP references to pages serving as DMA buffers needed for a > >> long time, no special synchronization with page_mkclean() or munmap() > >> => needs FOLL_PIN | FOLL_LONGTERM > >> This case has also a special case when the pages are actually DAX. Then > >> the caller additionally needs file lease and additional file_pin > >> structure is used for tracking this usage. > >> 3) ODP case - GUP references to pages serving as DMA buffers, MMU notifiers > >> used to synchronize with page_mkclean() and munmap() => normal page > >> references are fine. > > IMHO the munlock lesson told us about another one, that's in the end equivalent > to 3) > > 4) pinning for struct page manipulation only => normal page references > are fine Right, it's good to have this for clarity. > > I want to add that I'd like to convert users in cases 1) and 2) from using > > GUP to using differently named function. Users in case 3) can stay as they > > are for now although ultimately I'd like to denote such use cases in a > > special way as well... > > So after 1/2/3 is renamed/specially denoted, only 4) keeps the current > interface? Well, munlock() code doesn't even use GUP, just follow_page(). I'd wait to see what's left after handling cases 1), 2), and 3) to decide about the interface for the remainder. Honza -- Jan Kara SUSE Labs, CR