From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f198.google.com (mail-qt0-f198.google.com [209.85.216.198]) by kanga.kvack.org (Postfix) with ESMTP id B16326B0007 for ; Tue, 27 Feb 2018 02:10:32 -0500 (EST) Received: by mail-qt0-f198.google.com with SMTP id x30so6776176qtm.0 for ; Mon, 26 Feb 2018 23:10:32 -0800 (PST) Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com. [148.163.158.5]) by mx.google.com with ESMTPS id s66si3263020qkf.380.2018.02.26.23.10.31 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 26 Feb 2018 23:10:31 -0800 (PST) Received: from pps.filterd (m0098414.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w1R78rKY043139 for ; Tue, 27 Feb 2018 02:10:31 -0500 Received: from e06smtp11.uk.ibm.com (e06smtp11.uk.ibm.com [195.75.94.107]) by mx0b-001b2d01.pphosted.com with ESMTP id 2gcwfe2k6m-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Tue, 27 Feb 2018 02:10:31 -0500 Received: from localhost by e06smtp11.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 27 Feb 2018 07:10:28 -0000 Date: Tue, 27 Feb 2018 09:10:20 +0200 From: Mike Rapoport Subject: Re: [OMPI devel] [PATCH v5 0/4] vm: add a syscall to map a process memory into a pipe References: <1515479453-14672-1-git-send-email-rppt@linux.vnet.ibm.com> <20180220164406.3ec34509376f16841dc66e34@linux-foundation.org> <3122ec5a-7f73-f6b4-33ea-8c10ef32e5b0@virtuozzo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Message-Id: <20180227071020.GA24633@rapoport-lnx> Sender: owner-linux-mm@kvack.org List-ID: To: Nathan Hjelm Cc: Open MPI Developers , Andrei Vagin , Arnd Bergmann , Jann Horn , rr-dev@mozilla.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, Josh Triplett , criu@openvz.org, linux-mm@kvack.org, gdb@sourceware.org, Alexander Viro , Greg KH , linux-fsdevel@vger.kernel.org, Andrew Morton , Thomas Gleixner , Michael Kerrisk On Mon, Feb 26, 2018 at 09:38:19AM -0700, Nathan Hjelm wrote: > All MPI implementations have support for using CMA to transfer data > between local processes. The performance is fairly good (not as good as > XPMEM) but the interface limits what we can do with to remote process > memory (no atomics). I have not heard about this new proposal. What is > the benefit of the proposed calls over the existing calls? The proposed system call call that combines functionality of process_vm_read and vmsplice [1] and it's particularly useful when one needs to read the remote process memory and then write it to a file descriptor. In this case a sequence of process_vm_read() + write() calls that involves two copies of data can be replaced with process_vm_splice() + splice() which does not involve copy at all. [1] https://lkml.org/lkml/2018/1/9/32 > -Nathan > > > On Feb 26, 2018, at 2:02 AM, Pavel Emelyanov wrote: > > > > On 02/21/2018 03:44 AM, Andrew Morton wrote: > >> On Tue, 9 Jan 2018 08:30:49 +0200 Mike Rapoport wrote: > >> > >>> This patches introduces new process_vmsplice system call that combines > >>> functionality of process_vm_read and vmsplice. > >> > >> All seems fairly strightforward. The big question is: do we know that > >> people will actually use this, and get sufficient value from it to > >> justify its addition? > > > > Yes, that's what bothers us a lot too :) I've tried to start with finding out if anyone > > used the sys_read/write_process_vm() calls, but failed :( Does anybody know how popular > > these syscalls are? If its users operate on big amount of memory, they could benefit from > > the proposed splice extension. > > > > -- Pavel -- Sincerely yours, Mike. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org