Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754626Ab3JYPqw (ORCPT ); Fri, 25 Oct 2013 11:46:52 -0400 Received: from e28smtp07.in.ibm.com ([122.248.162.7]:39067 "EHLO e28smtp07.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754499Ab3JYPqp (ORCPT ); Fri, 25 Oct 2013 11:46:45 -0400 From: Robert 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 Jennings , Matt Helsley , Anthony Liguori , Michael Roth , Lei Li , Leonardo Garcia , Simon Jin , Vlastimil Babka Subject: [PATCH v2 0/2] vmpslice support for zero-copy gifting of pages Date: Fri, 25 Oct 2013 10:46:22 -0500 Message-Id: <1382715984-10558-1-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: 13102515-8878-0000-0000-0000096EA7F8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2552 Lines: 60 From: Robert C Jennings 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/2013-10/msg02787.html Changes from V1: - Cleanup zap coalescing in splice_to_pipe for readability - Field added to struct partial_page in v1 was unnecessary, using private field instead. - Read-side code in pipe_to_user pulled out into a new function - Improved documentation of read-side flipping code - Fixed locking issue in read-size flipping code found by sparse - Updated vmsplice comments for vmsplice_to_user(), vmsplice_to_pipe, and vmsplice syscall _______________________________________________________ vmsplice: unmap gifted pages for recipient vmsplice: Add limited zero copy to vmsplice fs/splice.c | 159 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 150 insertions(+), 9 deletions(-) -- 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/