RE: tmem - really default to on?

["Jan Beulich" <JBeulich@novell.com>]

>>> Dan Magenheimer <dan.magenheimer@oracle.com> 29.01.10 21:03 >>>
>I don't see how tmem could be causing this problem because it shouldn't
>even be in use (even with tmem=1) unless the domains in use call it.

We have the tmem kernel side patch in place, so any domain using our
kernel and a tmem-enabled file system would (potentially) use it.

>And the tmem code that limits to single page allocation should IIRC
>only be invoked once all system memory has been absorbed (which
>I suppose could be the case for dom0 when dom0_mem is not specified?)

Or if enough VMs had been created to consume all freely available
(outside of tmem) memory.

As said in the original mail - we have seen systems with more than 2G
"freeable" memory still causing domain creation to fail with "not enough
memory".

>I *think* maybe non-pvops dom0 has it on, but pvops almost certainly
>does not.

Correct - and our kernel is non-pvops.

>Rather than turn it off in Xen, maybe best solution is to turn it
>off in non-pvops dom0, at least by default.  Or really there's
>no reason it needs to be on for dom0 at all, so Xen code could
>check for dom0 and disable it if dom0.

I don't know that much about tmem, but why would Dom0 not benefit
from it being enabled if there's memory available in Xen?

Jan