Re: xen: memory initialization/balloon fixes (#3)

[David Vrabel <david.vrabel@citrix.com>]

On 20/09/11 17:57, Dan Magenheimer wrote:
>
> Thanks for your patches!  I am looking at a memory capacity/ballooning
> weirdness that I hoped your patchset might fix, but so far it has not.
> I'm wondering if there was an earlier fix that you are building upon
> and that I am missing.
> 
> My problem occurs in a PV domU with an upstream-variant kernel based
> on 3.0.5.  The problem is that the total amount of memory as seen
> from inside the guest is always substantially less than the amount
> of memory seen from outside the guest.  The difference seems to
> be fixed within a given boot, but assigning a different vm.cfg mem=
> changes the amount.  (For example, the difference D is about 18MB on
> a mem=128 boot and about 36MB on a mem=1024 boot.)

I don't see the problem?

The MemTotal value /proc/meminfo doesn't include some pages reserved by
the kernel which is why it's less than the maximum reservation of the
domain.

> Part B of the problem (and the one most important to me) is that
> setting /sys/devices/system/xen_memory/xen_memory0/target_kb
> to X results in a MemTotal inside the domU (as observed by
> "head -1 /proc/meminfo") of X-D.  This can be particularly painful
> when X is aggressively small as X-D may result in OOMs.
> To use kernel function/variable names (and I observed this with
> some debugging code), when balloon_set_new_target(X) is called
> totalram_pages gets driven to X-D.

Again, this looks like the correct behavior to me.

David