From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with SMTP id 510736B0089 for ; Wed, 4 Nov 2009 08:44:48 -0500 (EST) Date: Wed, 4 Nov 2009 15:41:47 +0200 From: "Michael S. Tsirkin" Subject: Re: [PATCHv7 3/3] vhost_net: a kernel-level virtio server Message-ID: <20091104134146.GE8920@redhat.com> References: <20091103172422.GD5591@redhat.com> <878wema6o0.fsf@basil.nowhere.org> <20091104121009.GF8398@redhat.com> <20091104125957.GL31511@one.firstfloor.org> <20091104130828.GC8920@redhat.com> <20091104131533.GM31511@one.firstfloor.org> <20091104131735.GD8920@redhat.com> <20091104133728.GN31511@one.firstfloor.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20091104133728.GN31511@one.firstfloor.org> Sender: owner-linux-mm@kvack.org To: Andi Kleen Cc: netdev@vger.kernel.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, mingo@elte.hu, linux-mm@kvack.org, akpm@linux-foundation.org List-ID: On Wed, Nov 04, 2009 at 02:37:28PM +0100, Andi Kleen wrote: > On Wed, Nov 04, 2009 at 03:17:36PM +0200, Michael S. Tsirkin wrote: > > On Wed, Nov 04, 2009 at 02:15:33PM +0100, Andi Kleen wrote: > > > On Wed, Nov 04, 2009 at 03:08:28PM +0200, Michael S. Tsirkin wrote: > > > > On Wed, Nov 04, 2009 at 01:59:57PM +0100, Andi Kleen wrote: > > > > > > Fine? > > > > > > > > > > I cannot say -- are there paths that could drop the device beforehand? > > > > > > > > Do you mean drop the mm reference? > > > > > > No the reference to the device, which owns the mm for you. > > > > The device is created when file is open and destroyed > > when file is closed. So I think the fs code handles the > > reference counting for me: it won't call file cleanup > > callback while some userspace process has the file open. > > Right? > > Yes. > > But the semantics when someone inherits such a fd through exec > or through file descriptor passing would be surely "interesting" > You would still do IO on the old VM. > > I guess it would be a good way to confuse memory accounting schemes > or administrators @) > It would be all saner if this was all a single atomic step. > > -Andi I have this atomic actually. A child process will first thing do SET_OWNER: this is required before any other operation. SET_OWNER atomically (under mutex) does two things: - check that there is no other owner - get mm and set current process as owner I hope this addresses your concern? -- MST -- 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