Re: [Xen-devel] [Patch RFC 00/13] VT-d Asynchronous Device-TLB Flush for ATS Device

["Xu, Quan" <quan.xu@xxxxxxxxx>]

>> >>> On 13.10.2015 at 22:50 <JBeulich@xxxxxxxx> wrote:
> >>> On 13.10.15 at 16:29, <quan.xu@xxxxxxxxx> wrote:
> >> > >>>On 29.09.2015 at 15:22 <JBeulich@xxxxxxxx> wrote:
> >> >>> On 29.09.15 at 04:53, <quan.xu@xxxxxxxxx> wrote:
> >> >>>> Monday, September 28, 2015 2:47 PM,<JBeulich@xxxxxxxx> wrote:
> >> >> >>> On 28.09.15 at 05:08, <quan.xu@xxxxxxxxx> wrote:
> >> >> >>>> Thursday, September 24, 2015 12:27 AM, Tim Deegan wrote:

> > 1. if (page->count_info & PGC_count_mask == 0) and (page->count_info
> > != 0) In this case, can the page be freed to xen domain heap?
> 
> Whether a page can get freed depends on changes to count_info, not just its
> current state. For instance, PGC_allocated set implies
> page->count_info & PGC_count_mask != 0, i.e. your question above
> cannot be answered properly. Just look at put_page() - it frees the page when
> the count _drops_ to zero.
> 
> > 2. if  (page->count_info & PGC_count_mask == 0) and
> (page->u.inuse.type_info != 0) :
> > In this case, can the page be freed to xen domain heap?
> 
> Generally type_info should be zero when the ref count is zero; there are, I 
> think,
> exceptional cases (like during domain death) where this might get violated 
> with
> no harm. But again - look at put_page() and you'll see that type_info doesn't
> matter for whether a page gets freed; all it matter is whether a page's type 
> can
> change: Only when type count is zero.
> 

Jan, Thanks for kind explanation.

-Quan

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