Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755729Ab3JGUWA (ORCPT ); Mon, 7 Oct 2013 16:22:00 -0400 Received: from e23smtp02.au.ibm.com ([202.81.31.144]:43172 "EHLO e23smtp02.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753276Ab3JGUV6 (ORCPT ); Mon, 7 Oct 2013 16:21:58 -0400 From: Robert C Jennings To: linux-kernel@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Alexander Viro , Rik van Riel , Andrea Arcangeli , Dave Hansen , Robert C Jennings , Matt Helsley , Anthony Liguori , Michael Roth , Lei Li , Leonardo Garcia , Vlastimil Babka Subject: [PATCH 0/2] vmpslice support for zero-copy gifting of pages Date: Mon, 7 Oct 2013 15:21:31 -0500 Message-Id: <1381177293-27125-1-git-send-email-rcj@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.1.2 X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13100720-5490-0000-0000-00000445A29E Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2163 Lines: 50 This patch set would add the ability to move anonymous user pages from one process to another through vmsplice without copying data. Moving pages rather than copying is implemented for a narrow case in this RFC to meet the needs of QEMU's usage (below). Among the restrictions the source address and destination addresses must be page aligned, the size argument must be a multiple of page size, and by the time the reader calls vmsplice, the page must no longer be mapped in the source. If a move is not possible the code transparently falls back to copying data. This comes from work in QEMU[1] to migrate a VM from one QEMU instance to another with minimal down-time for the VM. This would allow for an update of the QEMU executable under the VM. New flag usage This introduces use of the SPLICE_F_MOVE flag for vmsplice, previously unused. Proposed usage is as follows: Writer gifts pages to pipe, can not access original contents after gift: vmsplice(fd, iov, nr_segs, (SPLICE_F_GIFT | SPLICE_F_MOVE); Reader asks kernel to move pages from pipe to memory described by iovec: vmsplice(fd, iov, nr_segs, SPLICE_F_MOVE); Moving pages rather than copying is implemented for a narrow case in this RFC to meet the needs of QEMU's usage. If a move is not possible the code transparently falls back to copying data. For older kernels the SPLICE_F_MOVE would be ignored and a copy would occur. [1] QEMU localhost live migration: http://lists.gnu.org/archive/html/qemu-devel/2013-06/msg02540.html http://lists.gnu.org/archive/html/qemu-devel/2013-06/msg02577.html _______________________________________________________ vmsplice: Add limited zero copy to vmsplice vmsplice: unmap gifted pages for recipient fs/splice.c | 114 ++++++++++++++++++++++++++++++++++++++++++++++++- include/linux/splice.h | 1 + 2 files changed, 114 insertions(+), 1 deletion(-) -- 1.8.1.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/