From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Hubbard Subject: Re: [PATCH 1/1] infiniband/mm: convert put_page() to put_user_page*() Date: Thu, 23 May 2019 10:46:38 -0700 Message-ID: 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="utf-8"; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20190523173222.GH12145@mellanox.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Jason Gunthorpe , Ira Weiny Cc: "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 List-Id: linux-rdma@vger.kernel.org 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? thanks, -- John Hubbard NVIDIA