Re: [Xen-devel] [PATCH v7 4/5] ix86/ioreq server: Asynchronously reset outstanding p2m_ioreq_server entries.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 14.03.17 at 13:18, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:

> 
> On 3/14/2017 6:49 PM, Jan Beulich wrote:
>>>>> On 14.03.17 at 08:42, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
>>> On 3/13/2017 7:24 PM, Jan Beulich wrote:
>>>>>>> On 11.03.17 at 09:42, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
>>>>> On 3/11/2017 12:03 AM, Jan Beulich wrote:
>>>>>> But there's a wider understanding issue I'm having here: What is
>>>>>> an "entry" here? Commonly I would assume this to refer to an
>>>>>> individual (4k) page, but it looks like you really mean table entry,
>>>>>> i.e. possibly representing a 2M or 1G page.
>>>>> Well, it should be an entry pointing to a 4K page(only).
>>>>> For p2m_ioreq_server, we shall not meet huge page. Because they are
>>>>> changed from p2m_ram_rw pages
>>>>> in set_mem_type() -> p2m_change_type_one(), which calls p2m_set_entry()
>>>>> with PAGE_ORDER_4K specified.
>>>> And recombination of large pages won't ever end up hitting these?
>>> Well, by recombination I guess you refer to the POD pages? I do not
>>> think p2m_ioreq_server
>>> pages will be combined now, which means we do not need to worry about
>>> recounting the
>>> p2m_ioreq_server entries while a split happens.
>> No, I didn't think about PoD here. But indeed I was misremembering:
>> We don't currently make any attempt to transparently recreate large
>> pages.
> 
> Thanks Jan. So do you now think the current counting logic for 
> p2m_ioreq_server is correct? :-)

Yes. But please make sure you mention the 4k page dependency
at least in the commit message.

Jan


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