linux-kernel - Re: 3.0.0-rc2: Xen: High amount of kernel "reserved" memory, about 33% in 256MB DOMU [workaround included]

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Date:	Tue, 14 Jun 2011 23:37:27 +0200
From:	Tobias Diedrich <ranma+xen@...edrich.de>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:	xen-users@...ts.xensource.com, linux-kernel@...r.kernel.org
Subject: Re: 3.0.0-rc2: Xen: High amount of kernel "reserved" memory, about
 33% in 256MB DOMU [workaround included]

Konrad Rzeszutek Wilk wrote:
> On Tue, Jun 14, 2011 at 02:10:55AM +0200, Tobias Diedrich wrote:
> > Konrad Rzeszutek Wilk wrote:
> > > On Mon, Jun 13, 2011 at 10:50:03PM +0200, Tobias Diedrich wrote:
> > > > Hi,
> > > > 
> > > > another issue I'm seeing with 3.0-rc2 and Xen is that there is an
> > > > unexpectedly high amount of kernel reserved memory.
> > > 
> > > > 
> > > > I suspect that Linux allocates page table entries and corresponding
> > > > data structures for the whole 6GB areas of the provided 'physical
> > > > RAM map' even though it has rather big unusable holes in it.
> > > 
> > > Can you run it with 'memblock=debug debug loglevel=8 initcall_debug'?
> > > It should tell you where it tries (and for much space) the pagetables.
> 
> Ugh. In the meantime I would suggest you do the combination of:
> 
> Xen hypervisor line: "dom0_mem=max:512M" and on the Linux line: "mem=512M" to
> cut down on the extra pagetable creation..

That helps a bit on dom0, for a 256MB dom0 it brings free memory up
from 142MB
|Memory: 145576k/6028224k available (6122k kernel code, 3932612k absent, 1950036k reserved, 4761k data, 576k init)
to 173MB
|Memory: 177156k/262144k available (6122k kernel code, 452k absent, 84536k reserved, 4761k data, 576k init)

To shrink it more maybe the acpi tables would have to be moved...

-- 
Tobias						PGP: http://8ef7ddba.uguu.de
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