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[79.242.60.111]) by smtp.gmail.com with ESMTPSA id k13sm13145587wri.6.2021.12.19.09.44.05 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 19 Dec 2021 09:44:12 -0800 (PST) Message-ID: Date: Sun, 19 Dec 2021 18:44:03 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 To: Linus Torvalds , Nadav Amit Cc: Jason Gunthorpe , Linux Kernel Mailing List , Andrew Morton , Hugh Dickins , David Rientjes , Shakeel Butt , John Hubbard , Mike Kravetz , Mike Rapoport , Yang Shi , "Kirill A . Shutemov" , Matthew Wilcox , Vlastimil Babka , Jann Horn , Michal Hocko , Rik van Riel , Roman Gushchin , Andrea Arcangeli , Peter Xu , Donald Dutile , Christoph Hellwig , Oleg Nesterov , Jan Kara , Linux-MM , "open list:KERNEL SELFTEST FRAMEWORK" , "open list:DOCUMENTATION" References: <54c492d7-ddcd-dcd0-7209-efb2847adf7c@redhat.com> <20211217204705.GF6385@nvidia.com> <2E28C79D-F79C-45BE-A16C-43678AD165E9@vmware.com> <20211218030509.GA1432915@nvidia.com> <5C0A673F-8326-4484-B976-DA844298DB29@vmware.com> <20211218184233.GB1432915@nvidia.com> <5CA1D89F-9DDB-4F91-8929-FE29BB79A653@vmware.com> <4D97206A-3B32-4818-9980-8F24BC57E289@vmware.com> <5A7D771C-FF95-465E-95F6-CD249FE28381@vmware.com> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH v1 06/11] mm: support GUP-triggered unsharing via FAULT_FLAG_UNSHARE (!hugetlb) In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=YROacnvr; spf=none (imf29.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.129.124) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspamd-Queue-Id: 90681120040 X-Stat-Signature: phn4ysqobs53jhozb945x5bn9miqupgb X-Rspamd-Server: rspam04 X-HE-Tag: 1639935853-431173 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: > > Btw, the extra bit doesn't really have to be in the page tables. It > could be a bit in the page itself. We could add another page bit that > we just clear when we do the "add ref to page as you make a virtual > copy during fork() etc". ^ I'm playing with the idea if using a page bit to express: "This page is exclusive". On a CoW fault, if that bit is set, I can simply reuse the page. The semantics under which semantics to set the bit are slightly different than what you describe, and I'm playing with additional unsharing (on GUP R/O) that avoids mapping the copied page similarly R/O and simply sets the bit. But the general idea could fly I think, devil's in the detail ... -- Thanks, David / dhildenb