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

[Daniel P. Berrange]

On Fri, Nov 25, 2016 at 05:12:41PM +0100, Martin Kletzander wrote:
> On Fri, Nov 25, 2016 at 03:39:17PM +0000, Daniel P. Berrange wrote:
> > 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 ?
> > 
> 
> We have one, which we return for Get APIs that means that the setting
> was not restricted.  We would need to have a cgroup which we set to
> some huge value and then read it, store it and compare it all the time.
> It _should_ work as far as I can tell.

No, I meant can we use some constants

 #define UNLIMTED_VALUE_KERNEL_A_B_C 2343243245325
 #define UNLIMTED_VALUE_KERNEL_D_E_F 3253253253253253
 #define UNLIMTED_VALUE_KERNEL_G_H_I 325325325325232


 if kver == A_B_C && value == UNLIMTED_VALUE_KERNEL_A_B_C
      value = VIR_DOMAIN_MEMORY_PARAM_UNLIMITED
 else if kver == D_E_F && value == UNLIMTED_VALUE_KERNEL_D_E_F
      value = VIR_DOMAIN_MEMORY_PARAM_UNLIMITED
 else if kver == G_H_I && value == UNLIMTED_VALUE_KERNEL_G_H_I
      value = VIR_DOMAIN_MEMORY_PARAM_UNLIMITED


Regards,
Daniel
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