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

[Bob Liu <bob.liu@oracle.com>]

On 05/19/2014 07:34 PM, Jan Beulich wrote:
>>>> On 19.05.14 at 04:57, <lliubbo@gmail.com> 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.

-- 
Regards,
-Bob