Re: [Xen-devel] [PATCH 1 of 4] Improve ring management for memory events

["Andres Lagar-Cavilla" <andres@xxxxxxxxxxxxxxxx>]

> On Wed, Nov 23, Andres Lagar-Cavilla wrote:
>
>> Well, we can tone down printk's to be debug level. I don't think they're
>> unnecessary if they're made an optional debug tool.
>
> There is nothing to debug here, since the callers have to retry anyway.
>
>> Question: I have one vcpu, how do I fill up the ring quickly? (outside
>> of
>> foreign mappings)
>
> Have a balloon driver in the guest and balloon down more than
> 64*PAGE_SIZE. This is the default at least in my setup where the kernel
> driver releases some memory right away (I havent checked where this is
> actually configured).

I see, a guest can call decrease_reservation with an extent_order large
enough that it will overflow the ring. No matter the size of the ring.
Isn't preemption of this hypercall a better tactic than putting the vcpu
on a wait-queue? This won't preclude the need for wait queues, but it
feels like a much cleaner solution.

With retrying of foreign mappings in xc_map_foreign_bulk (and grants), I
wonder if we should put events in the ring due to foreign mappings *at
all*, in the case of congestion. Eventually a retry will get to kick the
pager.

Andres

>
> Olaf
>



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