From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tim Deegan Subject: Re: [PATCH 1 of 4] Prevent low values of max_pages for domains doing sharing or paging Date: Thu, 16 Feb 2012 14:58:37 +0000 Message-ID: <20120216145837.GA41163@ocelot.phlegethon.org> References: <11fd4e0a1e1a76ca3bc1.1329364624@xdev.gridcentric.ca> <20120216102014.GA40020@ocelot.phlegethon.org> <5612c7c996f87bb6a0e864258766e926.squirrel@webmail.lagarcavilla.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <5612c7c996f87bb6a0e864258766e926.squirrel@webmail.lagarcavilla.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: Andres Lagar-Cavilla Cc: xen-api@lists.xensource.com, andres@gridcentric.ca, xen-devel@lists.xensource.com, adin@gridcentric.ca List-Id: xen-devel@lists.xenproject.org At 06:45 -0800 on 16 Feb (1329374751), Andres Lagar-Cavilla wrote: > Fair enough (also referring to Jan's comments). We would be building > policy into the hypervisor. > > But I've seen squeezed set criminally low max_pages value (i.e. 256). > Granted, this is squeezed's problem, but shouldn't some sanity checking be > wired into the hypervisor? Some operating systems do just fine in 640K. :) But seriously, what lower limit would we use? Stupidly low max_pages for some uses would be just fine for others. > Why should we even allow max_pages < tot_pages? The reasoning is: - the tools want a hard guarantee that a rogue balloon driver can't mess up their calculations of how much free RAM there is. - when a VM is ballooning down we don't want to have the tools spinning watching actual max_pages and adjusting tot_pages down as it changes. It's not a particularly nice interface, though, and I'd be happy to see it revert to the old one (where new max had to be <= current tot). But that will need a fix for Xapi/squeezed to handle the ballooning-down case some other way. Cc-ing xen-API. Any XCP folks got an opinion about this? Would it be easy to make squeezed not need this behaviour? Cheers, Tim.