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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=unavailable 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 2FB53C282E1 for ; Thu, 23 May 2019 19:03:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 104762177E for ; Thu, 23 May 2019 19:03:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387437AbfEWTDc (ORCPT ); Thu, 23 May 2019 15:03:32 -0400 Received: from mga06.intel.com ([134.134.136.31]:61396 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387414AbfEWTDc (ORCPT ); Thu, 23 May 2019 15:03:32 -0400 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga104.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 23 May 2019 12:03:30 -0700 X-ExtLoop1: 1 Received: from iweiny-desk2.sc.intel.com ([10.3.52.157]) by orsmga008.jf.intel.com with ESMTP; 23 May 2019 12:03:30 -0700 Date: Thu, 23 May 2019 12:04:24 -0700 From: Ira Weiny To: John Hubbard Cc: Jason Gunthorpe , "john.hubbard@gmail.com" , Andrew Morton , "linux-mm@kvack.org" , LKML , "linux-rdma@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , Doug Ledford , Mike Marciniszyn , Dennis Dalessandro , Christian Benvenuti , Jan Kara Subject: Re: [PATCH 1/1] infiniband/mm: convert put_page() to put_user_page*() Message-ID: <20190523190423.GA19578@iweiny-DESK2.sc.intel.com> References: <20190523072537.31940-1-jhubbard@nvidia.com> <20190523072537.31940-2-jhubbard@nvidia.com> <20190523172852.GA27175@iweiny-DESK2.sc.intel.com> <20190523173222.GH12145@mellanox.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.11.1 (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 23, 2019 at 10:46:38AM -0700, John Hubbard wrote: > On 5/23/19 10:32 AM, Jason Gunthorpe wrote: > > On Thu, May 23, 2019 at 10:28:52AM -0700, Ira Weiny wrote: > > > > @@ -686,8 +686,8 @@ int ib_umem_odp_map_dma_pages(struct ib_umem_odp *umem_odp, u64 user_virt, > > > > * ib_umem_odp_map_dma_single_page(). > > > > */ > > > > if (npages - (j + 1) > 0) > > > > - release_pages(&local_page_list[j+1], > > > > - npages - (j + 1)); > > > > + put_user_pages(&local_page_list[j+1], > > > > + npages - (j + 1)); > > > > > > I don't know if we discussed this before but it looks like the use of > > > release_pages() was not entirely correct (or at least not necessary) here. So > > > I think this is ok. > > > > Oh? John switched it from a put_pages loop to release_pages() here: > > > > commit 75a3e6a3c129cddcc683538d8702c6ef998ec589 > > Author: John Hubbard > > Date: Mon Mar 4 11:46:45 2019 -0800 > > > > RDMA/umem: minor bug fix in error handling path > > 1. Bug fix: fix an off by one error in the code that cleans up if it fails > > to dma-map a page, after having done a get_user_pages_remote() on a > > range of pages. > > 2. Refinement: for that same cleanup code, release_pages() is better than > > put_page() in a loop. > > > > And now we are going to back something called put_pages() that > > implements the same for loop the above removed? > > > > Seems like we are going in circles?? John? > > > > put_user_pages() is meant to be a drop-in replacement for release_pages(), > so I made the above change as an interim step in moving the callsite from > a loop, to a single call. > > And at some point, it may be possible to find a way to optimize put_user_pages() > in a similar way to the batching that release_pages() does, that was part > of the plan for this. > > But I do see what you mean: in the interim, maybe put_user_pages() should > just be calling release_pages(), how does that change sound? I'm certainly not the expert here but FWICT release_pages() was originally designed to work with the page cache. aabfb57296e3 mm: memcontrol: do not kill uncharge batching in free_pages_and_swap_cache But at some point it was changed to be more general? ea1754a08476 mm, fs: remove remaining PAGE_CACHE_* and page_cache_{get,release} usage ... and it is exported and used outside of the swapping code... and used at lease 1 place to directly "put" pages gotten from get_user_pages_fast() [arch/x86/kvm/svm.c] >From that it seems like it is safe. But I don't see where release_page() actually calls put_page() anywhere? What am I missing? Ira