From mboxrd@z Thu Jan 1 00:00:00 1970 From: Olaf Hering Subject: Re: [PATCH 4 of 4] xenpaging: initial libxl support Date: Thu, 12 Jan 2012 15:12:35 +0100 Message-ID: <20120112141235.GB8324@aepfle.de> References: <20111120182951.GA4830@aepfle.de> <20111121151359.GA22981@aepfle.de> <20120109192119.GB10630@aepfle.de> <1326196936.5154.39.camel@elijah> <20120111145821.GA28944@aepfle.de> <20120111161023.GD81891@ocelot.phlegethon.org> <20120111163803.GA30142@aepfle.de> <20120111165855.GE81891@ocelot.phlegethon.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20120111165855.GE81891@ocelot.phlegethon.org> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Tim Deegan Cc: George Dunlap , "xen-devel@lists.xensource.com" , George Dunlap , Stefano Stabellini , Ian Campbell List-Id: xen-devel@lists.xenproject.org On Wed, Jan 11, Tim Deegan wrote: > At 17:38 +0100 on 11 Jan (1326303483), Olaf Hering wrote: > > On Wed, Jan 11, Tim Deegan wrote: > > > > > > Isnt that up to the host admin to decide where to take the memory from? > > > > So if its acceptable to swap parts of a VM (independent from what the > > > > guest OS thinks it has), so be it. > > > > > > Why? The _only_ reason I can imagine for wanting to use paging is when > > > the balloon driver can't or won't do its job. There's no advantage to > > > paging except that you can always force it to happen. > > > > Isnt that the whole point of paging, to make it happen at will without > > the guest (or the application at process level) noticing it? > > Yes, but that's a _bad_ thing. :) If the guest can co-operate, you'll > get way better eviction choices, better performance, and better > accounting (since the I/O is done by the guest to guest-owned disk). Hmm, I think its slightly like an 'rm -rf *' accident: bad, but allowed. > That's why I think both mechanisms should be visible up to the libxl > layer, but xl itself should just implement the one sensible policy: > try ballooning first, then page if that fails. So you are saying xl should take care of an improved mem-set command? Perhaps by tweaking memory/target first, monitoring something like tot_pages, and if memory/target isnt reached after some time, tweak memory/target-tot_pages so that xenpaging takes care of the rest? Olaf