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[142.162.115.133]) by smtp.gmail.com with ESMTPSA id u10sm1059825qtb.24.2021.01.15.10.40.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 15 Jan 2021 10:40:07 -0800 (PST) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1l0U10-001hs5-Uq; Fri, 15 Jan 2021 14:40:06 -0400 Date: Fri, 15 Jan 2021 14:40:06 -0400 From: Jason Gunthorpe To: Pavel Tatashin Cc: LKML , linux-mm , Andrew Morton , Vlastimil Babka , Michal Hocko , David Hildenbrand , Oscar Salvador , Dan Williams , Sasha Levin , Tyler Hicks , Joonsoo Kim , mike.kravetz@oracle.com, Steven Rostedt , Ingo Molnar , Peter Zijlstra , Mel Gorman , Matthew Wilcox , David Rientjes , John Hubbard , Linux Doc Mailing List , Ira Weiny , linux-kselftest@vger.kernel.org Subject: Re: [PATCH v4 08/10] mm/gup: limit number of gup migration failures, honor failures Message-ID: <20210115184006.GH4605@ziepe.ca> References: <20201217185243.3288048-1-pasha.tatashin@soleen.com> <20201217185243.3288048-9-pasha.tatashin@soleen.com> <20201217205048.GL5487@ziepe.ca> <20201218141927.GM5487@ziepe.ca> <20210113195528.GD4605@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Fri, Jan 15, 2021 at 01:10:27PM -0500, Pavel Tatashin wrote: > I've been thinking about this some more. Again, I am not sure this is > a bug. I understand split_huge_pmd() may split the PMD size page into > PTEs and leave the compound page intact. However, in order for pages[] > to have non sequential addresses in compound page, those PTEs must > also be migrated after split_huge_pmd(), Why focus on migrated? Anything could happen to those PTEs: they could be COW'd, they could be mmap/munmap'd, etc. Jason