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[99.254.144.39]) by smtp.gmail.com with ESMTPSA id a16-20020a05620a125000b00767502e8601sm3513396qkl.35.2023.07.31.11.51.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 31 Jul 2023 11:51:29 -0700 (PDT) Date: Mon, 31 Jul 2023 14:51:27 -0400 From: Peter Xu To: Linus Torvalds Cc: David Hildenbrand , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Andrew Morton , liubo , Matthew Wilcox , Hugh Dickins , Jason Gunthorpe , John Hubbard , Mel Gorman Subject: Re: [PATCH v1 0/4] smaps / mm/gup: fix gup_can_follow_protnone fallout Message-ID: References: <20230727212845.135673-1-david@redhat.com> <412bb30f-0417-802c-3fc4-a4e9d5891c5d@redhat.com> <66e26ad5-982e-fe2a-e4cd-de0e552da0ca@redhat.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Queue-Id: 1F7EA140003 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: pb8xwdsy4wpdideinmp6iro517w1dbge X-HE-Tag: 1690829493-636895 X-HE-Meta: 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 jlINmMub MeIyp6Rj9CCTPrRpBExn37oCOWjkRPIQ7XOYdVBJwHmX4S/u5T1ueJPxhLgKTL+aeKiz1mwXXeKKOJ83mi2LRF5uTdYKyj5lVkfz8Qrf3PzM3T39TW5cSmp7P5EFdr9LESXv5LbT/L9p1cQD81Ni6AJIO4kKQKQLV894C+X7tw8/YnMs6HnqDf7qjlKYT21UAuqUD0ZofYDctaXrzszcKl3czrKBrQOT284la8a5aH87evvVF9BqVBBZQ/FJq+nV4ngOyXtHlXXilIZkaVeexR46ZoeslABAIPtSPPGhhCBQIds4AIuSYDpWmLmQCs+p9dl3Rbt9RQQNvniq9auY3t7f6jaWlIXSmPCdokTSv9IYH08zHl1Qy5RwuUHV5gIFD1cTy10dSCtnjZjQjkCdE0di8u+WnIUBJ1Mxg X-Bogosity: Ham, tests=bogofilter, spamicity=0.000038, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Jul 31, 2023 at 11:23:59AM -0700, Linus Torvalds wrote: > So GUP-fast can only look at the page table data, and as such *has* to > fail if the page table is inaccessible. > > But GUP in general? Why would it want to honor numa faulting? > Particularly by default, and _particularly_ for things like > FOLL_REMOTE. True. > > In fact, I feel like this is what the real rule should be: we simply > define that get_user_pages_fast() is about looking up the page in the > page tables. > > So if you want something that acts like a page table lookup, you use > that "fast" thing. It's literally how it is designed. The whole - and > pretty much only - point of it is that it can be used with no locking > at all, because it basically acts like the hardware lookup does. Unfortunately I think at least kvm (besides the rest..) relies not only on numa balancing but also fast-gup.. :-( Please refer to hva_to_pfn() where it even supports fast-gup-only HVA translation when atomic==true set. Thanks, -- Peter Xu