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[79.242.59.201]) by smtp.gmail.com with ESMTPSA id p25-20020a05600c205900b003f9b1131a90sm2591078wmg.23.2023.06.20.08.28.29 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 20 Jun 2023 08:28:30 -0700 (PDT) Message-ID: <7cd1db3f-9bdf-dc0b-692c-380a2fa14286@redhat.com> Date: Tue, 20 Jun 2023 17:28:28 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 Subject: Re: [PATCH v2 2/8] mm/hugetlb: Prepare hugetlb_follow_page_mask() for FOLL_PIN To: Peter Xu , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Andrea Arcangeli , Mike Rapoport , Matthew Wilcox , Vlastimil Babka , John Hubbard , "Kirill A . Shutemov" , James Houghton , Andrew Morton , Lorenzo Stoakes , Hugh Dickins , Mike Kravetz , Jason Gunthorpe References: <20230619231044.112894-1-peterx@redhat.com> <20230619231044.112894-3-peterx@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20230619231044.112894-3-peterx@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: A969CC0005 X-Stat-Signature: 5ix1s8uu591uhiuxkp64gfpna1mzqhki X-HE-Tag: 1687274935-518512 X-HE-Meta: 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 tRd6bO72 CTAVIX5EnDlEAy7xZcm0r/LWXGDuD4kvYJIJ5APldfxl1nkAxGi6Xp+UG6f5E3c3GKl7uP/CD87hnV3wLNg5yZlq1OWFcdx092K6afb40q1d/vXeH1jA0YxjrzHc0ORVezvoXMsAdYDV+TU5YURIktmoCXjiwJtp/DgFdOYvNXVhi2SJFibwnkUpJXNSHfED2Q/7KJVxL6WGEvqCDQ/b/ijecNh2xuyOTjJy7o0tV1xyePoNOhkLr6SfAkoqZlYl/Szr5wMitt0zUSXIRZ7wEizFpmqqNGmi6cncLwnKQfhWfN7Sar/bUsf1nE7gbcX3aN4fNL7Izui2z3VuZTmlYek2L0A0zdlVCfay0kRcQ4abKznlR6Fx+Srh3hVZKzJzJTdJXagyQw/RyB5gvATda/mECCrIqBFYwdhrrXLiaEjcNMz9ddqN+jXNnUBTIMMUdQWIG 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 20.06.23 01:10, Peter Xu wrote: > follow_page() doesn't use FOLL_PIN, meanwhile hugetlb seems to not be the > target of FOLL_WRITE either. However add the checks. > > Namely, either the need to CoW due to missing write bit, or proper CoR on > !AnonExclusive pages over R/O pins to reject the follow page. That brings > this function closer to follow_hugetlb_page(). > > So we don't care before, and also for now. But we'll care if we switch > over slow-gup to use hugetlb_follow_page_mask(). We'll also care when to > return -EMLINK properly, as that's the gup internal api to mean "we should > do CoR". Not really needed for follow page path, though. > > When at it, switching the try_grab_page() to use WARN_ON_ONCE(), to be > clear that it just should never fail. Oh, and does this comment really belong into this patch or am I confused? -- Cheers, David / dhildenb