From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with ESMTP id 6E89F6B006A for ; Sun, 12 Jul 2009 16:51:49 -0400 (EDT) MIME-Version: 1.0 Message-ID: Date: Sun, 12 Jul 2009 14:08:36 -0700 (PDT) From: Dan Magenheimer Subject: RE: [Xen-devel] Re: [RFC PATCH 0/4] (Take 2): transcendent memory ("tmem") for Linux In-Reply-To: <4A5A4AF2.40609@redhat.com> Content-Type: text/plain; charset=Windows-1252 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org To: Avi Kivity Cc: npiggin@suse.de, akpm@osdl.org, jeremy@goop.org, xen-devel@lists.xensource.com, tmem-devel@oss.oracle.com, kurt.hackel@oracle.com, Rusty Russell , linux-kernel@vger.kernel.org, dave.mccracken@oracle.com, linux-mm@kvack.org, sunil.mushran@oracle.com, alan@lxorguk.ukuu.org.uk, Anthony Liguori , Schwidefsky , Marcelo Tosatti , chris.mason@oracle.com, Balbir Singh List-ID: > >> Right, the transient uses of tmem when applied to disk objects > >> (swap/pagecache) are very similar to disk caches. Which is > >> why you can > >> get a very similar effect when caching your virtual disks; > >> this can be > >> done without any guest modification. > > > > Write-through backing and virtual disk cacheing offer a > > similar effect, but it is far from the same. >=20 > Can you explain how it differs for the swap case? Maybe I don't=20 > understand how tmem preswap works. The key differences I see are the "please may I store something" API and the fact that the reply (yes or no) can vary across time depending on the state of the collective of guests. Virtual disk cacheing requires the host to always say yes and always deliver persistence. I can see that this is less of a concern for KVM because the host can swap... though doesn't this hide information from the guest and potentially have split-brain swapping issues? (thanks for the great discussion so far... going offline mostly now for a few days) Dan -- 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