Re: [Xen-devel] A good way to speed up the xl destroy time(guest page scrubbing)

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.12.14 at 14:43, <bob.liu@xxxxxxxxxx> wrote:

> On 12/05/2014 08:24 PM, Jan Beulich wrote:
>>>>> On 05.12.14 at 11:00, <bob.liu@xxxxxxxxxx> wrote:
>>> 5. Potential workaround
>>> 5.1 Use per-cpu list in idle_loop()
>>> Delist a batch of pages from heap_list to a per-cpu list, then scrub the
>>> per-cpu list and free back to heap_list.
>>>
>>> But Jan disagree with this solution:
>>> "You should really drop the idea of removing pages temporarily.
>>> All you need to do is make sure a page being allocated and getting
>>> simultaneously scrubbed by another CPU won't get passed to the
>>> caller until the scrubbing finished."
>> 
>> So you don't mention any downsides to this approach. If there are
>> any, please name them. If there aren't, what's the reason not to
>> go this route?
> 
> The reason was what you suggested was not very specific, I still have no
> idea how to implement a patch which can "make sure a page being
> allocated and getting simultaneously scrubbed by another CPU won't get
> passed to the caller until the scrubbing finished".

The scrubbing code would need to mark the page, and the allocation
code would need to spin on such marked pages until the mark clears.

Jan


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