From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1Jyr6r-0001zL-2x
	for qemu-devel@nongnu.org; Wed, 21 May 2008 12:24:13 -0400
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1Jyr6p-0001x5-DS
	for qemu-devel@nongnu.org; Wed, 21 May 2008 12:24:12 -0400
Received: from [199.232.76.173] (port=42422 helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1Jyr6p-0001wq-7d
	for qemu-devel@nongnu.org; Wed, 21 May 2008 12:24:11 -0400
Received: from mail2.shareable.org ([80.68.89.115]:44467)
	by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32)
	(Exim 4.60) (envelope-from <jamie@shareable.org>) id 1Jyr6o-00051b-U8
	for qemu-devel@nongnu.org; Wed, 21 May 2008 12:24:11 -0400
Date: Wed, 21 May 2008 17:24:06 +0100
From: Jamie Lokier <jamie@shareable.org>
Subject: Re: [Qemu-devel] Re: [PATCH][v2] Align file accesses with cache=off
	(O_DIRECT)
Message-ID: <20080521162406.GA21501@shareable.org>
References: <4833DC3F.8000604@suse.de> <20080521122629.GA14416@shareable.org>
	<48341783.3060204@qumranet.com>
	<20080521134154.GA15210@shareable.org>
	<483429EB.7070705@codemonkey.ws> <48342F05.2090603@qumranet.com>
	<48343106.4070801@codemonkey.ws> <48343844.1050107@qumranet.com>
	<20080521153454.GB20527@shareable.org>
	<48344793.2020902@codemonkey.ws>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <48344793.2020902@codemonkey.ws>
Reply-To: qemu-devel@nongnu.org
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/pipermail/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Anthony Liguori <anthony@codemonkey.ws>
Cc: Blue Swirl <blauwirbel@gmail.com>, Laurent Vivier <Laurent.Vivier@bull.net>, qemu-devel@nongnu.org, Paul Brook <paul@codesourcery.com>

Anthony Liguori wrote:
> Actually, this is precisely what I'd like to do.  The key is to 
> mmap(MAP_PRIVATE) from the underling file directly into the guest's 
> memory.  Should be just as applicable to QEMU as KVM (although for KVM 
> we need mmu-notifiers first).

With QEMU, that would lead to a huge number of VMAs - different mmap
address regions.  Linux (or any host for all I know) doesn't handle
that well.

On Linux you could use remap_file_pages to avoid the VMA problem.

-- Jamie