Re: [Xen-devel] [RFC PATCH] xen: free_domheap_pages: delay page scrub to tasklet

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.05.14 at 04:14, <bob.liu@xxxxxxxxxx> wrote:

> On 05/19/2014 07:34 PM, Jan Beulich wrote:
>>>>> On 19.05.14 at 04:57, <lliubbo@xxxxxxxxx> wrote:
>>> This patch try to delay scrub_one_page() to a tasklet which will be 
>>> scheduled on
>>> all online physical cpus, so that it's much faster to return from 'xl/xm
>>> destroy xxx'.
>> 
>> At the price of impacting all other guests. I think this is too simplistic
>> an approach. For one, I think the behavior ought to be configurable
>> by the admin: Deferring the scrubbing means you can't use the
>> memory for creating a new guest right away. And then you should
>> be doing this only on idle CPUs, or (with care not to introduce
>> security issues nor exhaustion of the DMA region) on CPUs actively
>> requesting memory, where the request can't be fulfilled without using
>> some of the not yet scrubbed memory.
>> 
>> And btw., 10 min of cleanup time for 1Tb seems rather much
>> independent of the specific scrubber behavior - did you check
>> whether decreasing the rate at which relinquish_memory() calls
>> hypercall_preempt_check() wouldn't already reduce this be quite
>> a bit?
>> 
> 
> I tried to call hypercall_preempt_check() every 10000 page, but the time
> didn't get any reduced.

So if you have the system scrub 1Tb at boot (via suitable
dom0_mem=), how long does that take?

Jan


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