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Date: Sun, 26 May 2019 04:06:31 -0700 From: Matthew Wilcox <willy@...radead.org> To: john.hubbard@...il.com Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org, Jason Gunthorpe <jgg@...pe.ca>, LKML <linux-kernel@...r.kernel.org>, linux-rdma@...r.kernel.org, linux-fsdevel@...r.kernel.org, John Hubbard <jhubbard@...dia.com>, Doug Ledford <dledford@...hat.com>, Mike Marciniszyn <mike.marciniszyn@...el.com>, Dennis Dalessandro <dennis.dalessandro@...el.com>, Christian Benvenuti <benve@...co.com>, Jan Kara <jack@...e.cz>, Ira Weiny <ira.weiny@...el.com>, Jérôme Glisse <jglisse@...hat.com>, Jason Gunthorpe <jgg@...lanox.com>, Christoph Hellwig <hch@...radead.org> Subject: Re: [PATCH v2] infiniband/mm: convert put_page() to put_user_page*() On Fri, May 24, 2019 at 06:45:22PM -0700, john.hubbard@...il.com wrote: > For infiniband code that retains pages via get_user_pages*(), > release those pages via the new put_user_page(), or > put_user_pages*(), instead of put_page() I have no objection to this particular patch, but ... > This is a tiny part of the second step of fixing the problem described > in [1]. The steps are: > > 1) Provide put_user_page*() routines, intended to be used > for releasing pages that were pinned via get_user_pages*(). > > 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. > > 3) After (2) is complete, use get_user_pages*() and put_user_page*() to > implement tracking of these pages. This tracking will be separate from > the existing struct page refcounting. > > 4) Use the tracking and identification of these pages, to implement > special handling (especially in writeback paths) when the pages are > backed by a filesystem. Again, [1] provides details as to why that is > desirable. I thought we agreed at LSFMM that the future is a new get_user_bvec() / put_user_bvec(). This is largely going to touch the same places as step 2 in your list above. Is it worth doing step 2? One of the advantages of put_user_bvec() is that it would be quite easy to miss a conversion from put_page() to put_user_page(), but it'll be a type error to miss a conversion from put_page() to put_user_bvec().
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