Re: [Xen-users] ARM: xehheap_megabytes less than 32

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Fri, 2015-07-17 at 21:44 +0000, Chris (Christopher) Brand wrote:
> Hi,
> 
> I'm trying to reduce the memory footprint of Xen on my 2GB platform,
> and one place that seems like a good target is the xenheap, which
> defaults to 64MB, very little of which I've seen used so far. I found
> the command line xenheap_megabytes command-line option, and
> setting that to 32 helps, but if I set it to less than 32, Xen doesn't boot.
> I found 
> http://www.poppelgaard.com/adjusting-dom0-and-xenheap-settings-in-xenserver,
> which mentions that back in the days of Xen 3.3, xenheap defaulted
> to 16MB, which indicates that I'm not trying something totally
> ridiculous.

That was for x86, but no I don't think it is inherently ridiculous to
try and reduce the Xen heap quite substantially.

One thing you should check though is what happens to domheap allocations
when the domheap is empty but the xenheap still has pages. I have a
feeling that such allocations can be satisfied from the xenheap, at
least under some circumstances (depending on CONFIG_SEPARATE_XENHEAP?).

Rather than trying to unpick xen/common/page_alloc.c and the various
heaps/nodes it might be easier to just confirm experimentally...

WRT the 32mb limit, I wonder if that is the same underlying issue as you
tripped over for the frametable mapping?

Ian.



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