From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 200E8C04AAF for ; Thu, 16 May 2019 13:03:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F132520862 for ; Thu, 16 May 2019 13:03:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727152AbfEPNDE (ORCPT ); Thu, 16 May 2019 09:03:04 -0400 Received: from relay.sw.ru ([185.231.240.75]:51894 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727469AbfEPNDD (ORCPT ); Thu, 16 May 2019 09:03:03 -0400 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 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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