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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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?

Jan


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