From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: [Qemu-devel] [RFC PATCH 1/1] ceph/rbd block driver for qemu-kvm Date: Tue, 25 May 2010 11:21:25 -0500 Message-ID: <4BFBF905.1030901@codemonkey.ws> References: <20100519192222.GD61706@ncolin.muc.de> <4BF5A9D2.5080609@codemonkey.ws> <4BF91937.2070801@redhat.com> <4BFBAE46.5050801@redhat.com> <4BFBB3C1.9020905@redhat.com> <4BFBCFAC.9070807@codemonkey.ws> <4BFBD13C.60605@redhat.com> <4BFBD20E.5060207@codemonkey.ws> <4BFBD2D5.2000201@redhat.com> <4BFBD6CD.3000503@codemonkey.ws> <4BFBD82F.3020404@redhat.com> <4BFBD943.8020704@codemonkey.ws> <4BFBE614.9080306@redhat.com> <4BFBE64F.6020901@codemonkey.ws> <4BFBF7D4.80900@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Kevin Wolf , Blue Swirl , ceph-devel@vger.kernel.org, Christian Brunner , kvm@vger.kernel.org, qemu-devel@nongnu.org To: Avi Kivity Return-path: Received: from mail-gw0-f46.google.com ([74.125.83.46]:58517 "EHLO mail-gw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932154Ab0EYQVa (ORCPT ); Tue, 25 May 2010 12:21:30 -0400 In-Reply-To: <4BFBF7D4.80900@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 05/25/2010 11:16 AM, Avi Kivity wrote: > On 05/25/2010 06:01 PM, Anthony Liguori wrote: >> On 05/25/2010 10:00 AM, Avi Kivity wrote: >>> The latter. Why is it less important? If you don't inherit the >>> memory, you can't access it. >>> >>>> You can also pass /dev/shm fd's via SCM_RIGHTs to establish shared >>>> memory segments dynamically. >>> >>> Doesn't work for anonymous memory. >> >> What's wrong with /dev/shm memory? > > The kernel treats anonymous and nonymous memory differently for > swapping (see /proc/sys/vm/swappiness); transparent hugepages won't > work for /dev/shm (though it may be argued that that's a problem with > thp); setup (/dev/shm defaults to half memory IIRC, we want mem+swap); > different cgroup handling; somewhat clunky (a minor concern to be sure). Surely, with mmu notifiers, it wouldn't be that hard to share anonymous memory via an fd though, no? Regards, Anthony Liguori > > Nothing is a killer, but we should prefer anonymous memory. >