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[185.231.240.75]) by mx.google.com with ESMTPS id y7si4600696lfh.9.2019.05.16.06.03.00 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 16 May 2019 06:03:00 -0700 (PDT) Received-SPF: pass (google.com: domain of ktkhai@virtuozzo.com designates 185.231.240.75 as permitted sender) client-ip=185.231.240.75; Authentication-Results: mx.google.com; spf=pass (google.com: domain of ktkhai@virtuozzo.com designates 185.231.240.75 as permitted sender) smtp.mailfrom=ktkhai@virtuozzo.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=virtuozzo.com Received: from [172.16.25.169] by relay.sw.ru with esmtp (Exim 4.91) (envelope-from ) id 1hRG2D-0006j8-2v; Thu, 16 May 2019 16:02:57 +0300 Subject: Re: [PATCH RFC 0/5] mm: process_vm_mmap() -- syscall for duplication a process mapping To: Jann Horn Cc: Andrew Morton , Dan Williams , Michal Hocko , keith.busch@intel.com, "Kirill A . Shutemov" , pasha.tatashin@oracle.com, Alexander Duyck , ira.weiny@intel.com, Andrey Konovalov , arunks@codeaurora.org, Vlastimil Babka , Christoph Lameter , Rik van Riel , Kees Cook , hannes@cmpxchg.org, npiggin@gmail.com, Mathieu Desnoyers , shakeelb@google.com, Roman Gushchin , Andrea Arcangeli , Hugh Dickins , Jerome Glisse , Mel Gorman , daniel.m.jordan@oracle.com, kernel list , Linux-MM References: <155793276388.13922.18064660723547377633.stgit@localhost.localdomain> From: Kirill Tkhai Message-ID: <456c7367-0656-933b-986d-febdcc5ab98e@virtuozzo.com> Date: Thu, 16 May 2019 16:02:55 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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: Hi, Jann, On 15.05.2019 21:46, Jann Horn wrote: > On Wed, May 15, 2019 at 5:11 PM Kirill Tkhai wrote: >> This patchset adds a new syscall, which makes possible >> to clone a mapping from a process to another process. >> The syscall supplements the functionality provided >> by process_vm_writev() and process_vm_readv() syscalls, >> and it may be useful in many situation. >> >> For example, it allows to make a zero copy of data, >> when process_vm_writev() was previously used: > [...] >> This syscall may be used for page servers like in example >> above, for migration (I assume, even virtual machines may >> want something like this), for zero-copy desiring users >> of process_vm_writev() and process_vm_readv(), for debug >> purposes, etc. It requires the same permittions like >> existing proc_vm_xxx() syscalls have. > > Have you considered using userfaultfd instead? userfaultfd has > interfaces (UFFDIO_COPY and UFFDIO_ZERO) for directly shoving pages > into the VMAs of other processes. This works without the churn of > creating and merging VMAs all the time. userfaultfd is the interface > that was written to support virtual machine migration (and it supports > live migration, too). I know about userfaultfd, but it does solve the discussed problem. It allocates new pages to make UFFDIO_COPY (see mcopy_atomic_pte()), and it accumulates all the disadvantages, the example from [0/5] message has. Kirill