[libvirt] [PATCH V2] qemu: Redefine the "unlimited" memory limits one more time

[Daniel P. Berrange]

On Fri, Nov 25, 2016 at 04:35:14PM +0100, Martin Kletzander wrote:
> On Fri, Nov 25, 2016 at 03:19:54PM +0100, Viktor Mihajlovski wrote:
> > On 18.11.2016 17:44, Viktor Mihajlovski wrote:
> > > With kernel 3.18 (since commit 3e32cb2e0a12b6915056ff04601cf1bb9b44f967) the
> > > "unlimited" value for cgroup memory limits has changed once again as its byte
> > > value is now computed from a page counter.
> > > The new "unlimited" value reported by the cgroup fs is therefore 2**51-1 pages
> > > which is (VIR_DOMAIN_MEMORY_PARAM_UNLIMITED - 3072). This results e.g. in virsh
> > > memtune displaying 9007199254740988 instead of unlimited for the limits.
> > > 
> 
> Ah, I wonder hoe many times we'll have to deal with this.
> 
> Anyway, this means it is not enough to shift by 2 if the system hugepage
> is more than 4k (e.g. 2M).  I remember we had to change something due to
> such hosts.  virGetSystemPageSize(KB) should help with that.
> 
> We could also make it 2^50 - pagesize just to make sure it will work for
> a while, but some might not like it.

I guess I'm not understanding how this code copes with the fact that
we now have 3 different "unlimited" values to deal with.

Could we not simply record the unlimited values and pick the right
one based on kernel version we detect ?

Regards,
Daniel
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