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(p200300cbc7024b00c6fab613dbdc00ab.dip0.t-ipconnect.de. [2003:cb:c702:4b00:c6fa:b613:dbdc:ab]) by smtp.gmail.com with ESMTPSA id h7-20020a05600c314700b003f07ef4e3e0sm5879348wmo.0.2023.04.12.01.47.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 12 Apr 2023 01:47:53 -0700 (PDT) Message-ID: <27ac2f51-e2bf-7645-7a76-0684248a5902@redhat.com> Date: Wed, 12 Apr 2023 10:47:52 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.9.1 Subject: Re: RFC for new feature to move pages from one vma to another without split To: Peter Xu , Lokesh Gidra Cc: Axel Rasmussen , Andrew Morton , "open list:MEMORY MANAGEMENT" , linux-kernel , Andrea Arcangeli , "Kirill A . Shutemov" , "Kirill A. Shutemov" , Brian Geffon , Suren Baghdasaryan , Kalesh Singh , Nicolas Geoffray , Jared Duke , android-mm , Blake Caldwell , Mike Rapoport References: 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-Queue-Id: 198B6C0006 X-Rspamd-Server: rspam01 X-Stat-Signature: 3qg4pegnu7i9iex7iok793hd5twiyun9 X-HE-Tag: 1681289276-937327 X-HE-Meta: U2FsdGVkX1+Cp1YtHNScCo4ShJdQc8fr5I+FWEhXyskIXcTIXp+CSVJkcvKoBNCGY1tAC2I7JE7ThIvU4T2S4ghFu1wW4K5XJkbNtk9yg5fAx15vD8ytAKnb05/IAsriYSECalvjprQhRtXLWHLSZEvp0QZcz77hj7JcbNnCW3jkMGDOuUoTBXdmauibiKFKHreGzDsVTH46sg5SwwMIaTIVtw2/tQmi7vsgF++P30ZzQVAAGmR1vlBLTxo7bcfZcC6eNNZheA2nCjeMtIEbxg5YWznSSUmCjZvLzdiJ9FLpLgKXURlvYNlBBc/Y3IAvZ51pP7DYxlSOryrJwgRpaqv4Nqhu9TWZ2td696HM0V3C2O1jDmO4jDYg6fWo4bTFKoXGAI7R9d2KijanJGOvYh9qTPFGxKm/7K2zLRwRXqVm06SMxwlMsCRoycT2EPPv5o7WhsVeQeR3dSRYuIxs1IiGO+BIjHJ2b6zVDj0+YZJlxulpOqyzlqkn6q+09ZNqO/cm7b2rYhjHuGtR5A3RbxQOhxwy58skw8t8B20CZbFRJTDmDMvK7WYaFtVWa+HZO20QS5UZ6qYN+o0jyioPIS4hrkQECm5kzuvbRB2KMjfdbWlcY+VaeufBVWvZS+OiOnyaWtTrve5v0aDU5KmaXfsCr97dBfxgehZKPAA14o9e3qGoAv+j2JJQofm7Q+3RdoMiJfuuXRmbl/xQvVrUE87smIQ5lKRfWWcZ40afVZVWou2Z/K8zjrHPFnxPOkEVw0u/72uavQAWGF611G2wWLMofZJAI9cAjly694XWyON5le1vjzzxveIsoMNUj6jk8Q9A6Z8OdkookW5Pzig5hdRR9tq8Gmnnpnqvqp5/2iN13wggVWpNXFrODoWPqK4Z9ztsdwAyJuKB3GwLLGlkIm7PVpCQfXZHkirjZYv286Kb0gSA+VexBnbj94pu3Zl7JyfwKdvmBhkmD5967o9 3Ym5NJFy l/wID3z+JkT8pYvGu9KoxM7f5IejGtdicEbSYesxZchxlaYx82DiNOPkD3t7Op12QwAZecyGjxGoCY9+sR0N7mj8GfLYMs/3E0szRyP6qXARc59RepBI6ZRdbPoa3K5vxpvXeHUJsXY49xxUBuGqMAkrYWR1hGGg+4dKoUwEqttiQMp4+BDk77mbDRnooQlgV3A62bHJWW74TjZxnb1X62xLRTc5horMVOmHJrUFy3gQ3us6quvr4A974OxwLilzG6HA7NxQJF2ZhqdYmIAnVV1cM47BEu1RfjCBSNG5OchOSs3jxAjR/KoIQKCpIcFlYA8A4CJvw3lK5FCe1OxTPBwnRmhlap48L5nsjIzMOw4VF04joARrOLp4R+5WoB/iVrl92J0uWkRGFVNLjn1Zm50y6WNnQArT781zW6zrUoZKNjbvm01HKyt3KwLmVPEImnhHh09G6clPYOSndYtg23x57mA== 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 06.04.23 19:29, Peter Xu wrote: > Hi, Lokesh, > > Sorry for a late reply. Copy Blake Caldwell and Mike too. > > On Thu, Feb 16, 2023 at 02:27:11PM -0800, Lokesh Gidra wrote: >> I) SUMMARY: >> Requesting comments on a new feature which remaps pages from one >> private anonymous mapping to another, without altering the vmas >> involved. Two alternatives exist but both have drawbacks: >> 1. userfaultfd ioctls allocate new pages, copy data and free the old >> ones even when updates could be done in-place; >> 2. mremap results in vma splitting in most of the cases due to 'pgoff' mismatch. > > Personally it was always a mistery to me on how vm_pgoff works with > anonymous vmas and why it needs to be setup with vm_start >> PAGE_SHIFT. > > Just now I tried to apply below oneliner change: > > @@ -1369,7 +1369,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr, > /* > * Set pgoff according to addr for anon_vma. > */ > - pgoff = addr >> PAGE_SHIFT; > + pgoff = 0; > break; > default: > return -EINVAL; > > The kernel even boots without a major problem so far.. I think it's for RMAP purposes. Take a look at linear_page_index() and how it's, for example, used in ksm_might_need_to_copy() alongside page->index. -- Thanks, David / dhildenb