Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932381Ab3EBSEh (ORCPT ); Thu, 2 May 2013 14:04:37 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:27701 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759009Ab3EBSEg (ORCPT ); Thu, 2 May 2013 14:04:36 -0400 Date: Thu, 2 May 2013 14:04:04 -0400 From: Konrad Rzeszutek Wilk To: Stefano Stabellini Cc: Daniel Kiper , Ian Campbell , "carsten@schiers.de" , "darren.s.shepherd@gmail.com" , David Vrabel , Ian Jackson , "james-xen@dingwall.me.uk" , "linux-kernel@vger.kernel.org" , "xen-devel@lists.xensource.com" , "Keir (Xen.org)" , Dave.Scott@eu.citrix.com, Jonathan Ludlam Subject: Re: [PATCH v2 2/2] xen/balloon: Enforce various limits on target Message-ID: <20130502180404.GA16489@phenom.dumpdata.com> References: <1367235468-8360-1-git-send-email-daniel.kiper@oracle.com> <1367235468-8360-3-git-send-email-daniel.kiper@oracle.com> <1367246649.3142.316.camel@zakaz.uk.xensource.com> <20130430125952.GD9904@debian70-amd64.local.net-space.pl> <1367329458.3142.524.camel@zakaz.uk.xensource.com> <20130430185852.GF9904@debian70-amd64.local.net-space.pl> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-Source-IP: acsinet21.oracle.com [141.146.126.237] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2660 Lines: 54 On Thu, May 02, 2013 at 12:34:32PM +0100, Stefano Stabellini wrote: > On Tue, 30 Apr 2013, Daniel Kiper wrote: > > > > > > +/* > > > > > > + * Extra internal memory reserved by libxl. > > > > > > + * Check tools/libxl/libxl_memory.txt file in Xen source for more details. > > > > > > + */ > > > > > > +#define LIBXL_MAXMEM_CONSTANT_PAGES (1024 * 1024 / PAGE_SIZE) > > > > > > > > > > I think we need to find a way to achieve your aims which doesn't require > > > > > leaking internal implementation details of libxl into the guest kernels. > > > > > What happens if libxl decides to double this? > > > > > > > > I agree that this is not elegant solution. However, if we would like to > > > > be in line with docs/misc/libxl_memory.txt (this is correct path) this > > > > is a must. > > > > > > I'm not sure about this, that file describes the toolstacks view of the > > > memory in a system. That need not necessarily correspond with the > > > guest's ideas (although you would hope it would be a superset). > > > > > > Surely it is logically wrong to bake toolstack specific knowledge in the > > > guest? If someone can describe a meaningful semantic for this number in > > > a toolstack independent way then perhaps it would be appropriate to do > > > something with it. I've no idea, having looked at both the document and > > > the code, what this value actually is. > > > > This was added by commit 9905ac2b90a3e7cecd9e7dfe21c252362e7080b2 > > (libxenlight: implement libxl_set_memory_target). It was written > > by Keir and signed off by Stefano (both are CCed here). Guys, > > why did you added LIBXL_MAXMEM_CONSTANT? What does it mean? > > libxl inherits the memory model from xapi. > LIBXL_MAXMEM_CONSTANT corresponds to "extra internal" in xapi, an amount > of memory that is not allocated to the domain but it is left as a slack > on top of the actual memory target to determine the Xen maxmem. > I believe it comes from empirical measurements and stress testing on the > platform. What is this 'slack' used for? > The xapi guys, CC'ed, might have more insights on what exactly is. > > > I dislike having to pull this "hack" into Linux, but if it is actually > important to leave LIBXL_MAXMEM_CONSTANT unused, then it is worth doing. > I would add a big comment on top saying: > > "libxl seems to think that we need to leave LIBXL_MAXMEM_CONSTANT > kilobytes unused, let's be gentle and do that." -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/