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

[Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>]

On 3/14/2017 9:11 PM, Jan Beulich wrote:
> > > > 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.
OK. Will do.

Thanks
Yu
> Jan

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