Re: [Xen-devel] Proposed new "memory capacity claim" hypercall/feature

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 08.11.12 at 20:16, Dan Magenheimer <dan.magenheimer@xxxxxxxxxx> wrote:
>>  From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> >>> On 08.11.12 at 11:50, Keir Fraser <keir@xxxxxxx> wrote:
>> > On 08/11/2012 09:47, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
>> >> The only thing that indeed is - on non-preemptible kernels - done
>> >> only on exit to user mode is the eventual entering of the scheduler.
>> >
>> > That alone may still be an argument for restricting the batch size from the
>> > toolstack?
>> 
>> Yes, this clearly prohibits unlimited batches. But not being able to
>> schedule should be less restrictive than not being able to run
>> softirqs, so I'd still put under question whether the limit shouldn't
>> be bumped.
> 
> Wait, please define unlimited.

Unlimited as in unlimited.

> I think we are in agreement from previous discussion that, to solve
> the TOCTOU race, the heap_lock must be held for the entire allocation
> for a domain creation.  True?

That's only one way (and as Keir already responded, not one
that we should actually pursue).

The point about being fast enough was rather made to allow
a decision towards the feasibility of intermediately disabling
tmem (or at least allocations originating from it) in particular
(I'm not worried about micro-allocations - the tool stack has to
provide some slack in its calculations for this anyway).

Jan



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