From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f48.google.com (mail-pa0-f48.google.com [209.85.220.48]) by kanga.kvack.org (Postfix) with ESMTP id 05EF76B00DB for ; Fri, 25 Oct 2013 11:46:45 -0400 (EDT) Received: by mail-pa0-f48.google.com with SMTP id bj1so5359685pad.21 for ; Fri, 25 Oct 2013 08:46:45 -0700 (PDT) Received: from psmtp.com ([74.125.245.185]) by mx.google.com with SMTP id mj9si5464119pab.16.2013.10.25.08.46.43 for ; Fri, 25 Oct 2013 08:46:45 -0700 (PDT) Received: from /spool/local by e28smtp02.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 25 Oct 2013 21:16:40 +0530 Received: from d28relay01.in.ibm.com (d28relay01.in.ibm.com [9.184.220.58]) by d28dlp02.in.ibm.com (Postfix) with ESMTP id DAEEC394005A for ; Fri, 25 Oct 2013 21:16:16 +0530 (IST) Received: from d28av03.in.ibm.com (d28av03.in.ibm.com [9.184.220.65]) by d28relay01.in.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r9PFnVZe29294674 for ; Fri, 25 Oct 2013 21:19:32 +0530 Received: from d28av03.in.ibm.com (localhost [127.0.0.1]) by d28av03.in.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id r9PFkZTP019639 for ; Fri, 25 Oct 2013 21:16:35 +0530 From: Robert Jennings 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> Sender: owner-linux-mm@kvack.org List-ID: 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 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, 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