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[2003:cb:c706:6b00:bf49:f14b:380d:f871]) by smtp.gmail.com with ESMTPSA id i8-20020adfefc8000000b0030ada01ca78sm5634933wrp.10.2023.07.28.13.00.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 28 Jul 2023 13:00:54 -0700 (PDT) Message-ID: Date: Fri, 28 Jul 2023 22:00:53 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH v1 0/4] smaps / mm/gup: fix gup_can_follow_protnone fallout To: Peter Xu Cc: Linus Torvalds , 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 References: <20230727212845.135673-1-david@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: 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: rspam12 X-Rspamd-Queue-Id: CE0BA4000B X-Stat-Signature: xp84f8psomcxmxpga43gbem9pifyjxjd X-HE-Tag: 1690574458-254205 X-HE-Meta: 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 juCTTagK nh0nyO7jf8YBtrq88CfwqGCTFtpNyhl9uD/BcWiBnaU4VD5FYBis2+x7yeEAWYHxvnS+J0uZ1kr+8DvFrNAYnEmU6Yetl79tmJqZloTXFfQwVCZfnCrmpQTSwkM1rfigSs+f1tvzj3SMK986bE7GjV1sN6gmtYxMqRk/ejPiLwOPmwYo5inm55FWfUpQH7y9D8WANGlqTpqeBT0Aka7F76hFgVLDYt9QSawh4wZsZUwTTjgJJVAWF3+5l++0AP+dQEK+10PfTKsVT2eQwAjAwgGoINnu8VNeVbzCeZCmyZFgzHPT6GLz5NFw/0NRhwC2gtnmrVqNKzWrG2t7t06ODQBfx1HJkn0f2t6/EdI81/Ew0WzDAOjybquBJoUNW75DI1oTC+uxA+YdEFlI8WHMz9TjR0BZHLgUrckRbFaTWP7fHs5ViO7PMqtOJbA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 28.07.23 21:50, Peter Xu wrote: > On Fri, Jul 28, 2023 at 09:40:54PM +0200, David Hildenbrand wrote: >> Hmm. So three alternatives I see: >> >> 1) Use FOLL_FORCE in follow_page() to unconditionally disable protnone >> checks. Alternatively, have an internal FOLL_NO_PROTNONE flag if we >> don't like that. >> >> 2) Revert the commit and reintroduce unconditional FOLL_NUMA without >> FOLL_FORCE. >> >> 3) Have a FOLL_NUMA that callers like KVM can pass. > > I'm afraid 3) means changing numa balancing to opt-in, probably no-go for > any non-kvm gup users as that could start to break there, even if making > smaps/follow_page happy again. > > I keep worrying 1) on FOLL_FORCE abuse. > > So I keep my vote on 2). Linus had a point that we can nowadays always set FOLL_NUMA, even with FOLL_FORCE. ... so maybe we want to let GUP always set FOLL_NUMA (even with FOLL_FORCE) and follow_page() never set FOLL_NUMA. That would at least decouple FOLL_NUMA from FOLL_FORCE. -- Cheers, David / dhildenb