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[156.34.55.100]) by smtp.gmail.com with ESMTPSA id a21sm255229qkg.47.2019.07.02.18.15.23 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 02 Jul 2019 18:15:23 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1hiTrm-0004FU-T2; Tue, 02 Jul 2019 22:15:22 -0300 Date: Tue, 2 Jul 2019 22:15:22 -0300 From: Jason Gunthorpe To: ira.weiny@intel.com Cc: Andrew Morton , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org, =?utf-8?B?SsOpcsO0bWU=?= Glisse , Dan Williams , John Hubbard Subject: Re: [PATCH v4] mm/swap: Fix release_pages() when releasing devmap pages Message-ID: <20190703011522.GA15993@ziepe.ca> References: <20190605214922.17684-1-ira.weiny@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190605214922.17684-1-ira.weiny@intel.com> User-Agent: Mutt/1.9.4 (2018-02-28) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Jun 05, 2019 at 02:49:22PM -0700, ira.weiny@intel.com wrote: > From: Ira Weiny > > release_pages() is an optimized version of a loop around put_page(). > Unfortunately for devmap pages the logic is not entirely correct in > release_pages(). This is because device pages can be more than type > MEMORY_DEVICE_PUBLIC. There are in fact 4 types, private, public, FS > DAX, and PCI P2PDMA. Some of these have specific needs to "put" the > page while others do not. > > This logic to handle any special needs is contained in > put_devmap_managed_page(). Therefore all devmap pages should be > processed by this function where we can contain the correct logic for a > page put. > > Handle all device type pages within release_pages() by calling > put_devmap_managed_page() on all devmap pages. If > put_devmap_managed_page() returns true the page has been put and we > continue with the next page. A false return of > put_devmap_managed_page() means the page did not require special > processing and should fall to "normal" processing. > > This was found via code inspection while determining if release_pages() > and the new put_user_pages() could be interchangeable.[1] > > [1] https://lore.kernel.org/lkml/20190523172852.GA27175@iweiny-DESK2.sc.intel.com/ > > Cc: Jérôme Glisse > Cc: Michal Hocko > Reviewed-by: Dan Williams > Reviewed-by: John Hubbard > Signed-off-by: Ira Weiny > > --- > Changes from V3: > Update comment to the one provided by John > > Changes from V2: > Update changelog for more clarity as requested by Michal > Update comment WRT "failing" of put_devmap_managed_page() > > Changes from V1: > Add comment clarifying that put_devmap_managed_page() can still > fail. > Add Reviewed-by tags. > > mm/swap.c | 13 +++++++++---- > 1 file changed, 9 insertions(+), 4 deletions(-) Andrew, As per the discussion on the hmm thread I took this patch into the hmm.git as the conflict that was created with CH's rework was tricky - the resolution is simple, but keeping Ira's hunk instead of the delete is, IMHO, subtle. Regards, Jason