Messages in this thread | | | Date | Tue, 25 Jul 2017 17:32:00 +0800 | From | Wei Wang <> | Subject | Re: [PATCH v12 6/8] mm: support reporting free page blocks |
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On 07/24/2017 05:00 PM, Michal Hocko wrote: > On Wed 19-07-17 20:01:18, Wei Wang wrote: >> On 07/19/2017 04:13 PM, Michal Hocko wrote: > [... >>> All you should need is the check for the page reference count, no? I >>> assume you do some sort of pfn walk and so you should be able to get an >>> access to the struct page. >> Not necessarily - the guest struct page is not seen by the hypervisor. The >> hypervisor only gets those guest pfns which are hinted as unused. From the >> hypervisor (host) point of view, a guest physical address corresponds to a >> virtual address of a host process. So, once the hypervisor knows a guest >> physical page is unsued, it knows that the corresponding virtual memory of >> the process doesn't need to be transferred in the 1st round. > I am sorry, but I do not understand. Why cannot _guest_ simply check the > struct page ref count and send them to the hypervisor?
Were you suggesting the following? 1) get a free page block from the page list using the API; 2) if page->ref_count == 0, send it to the hypervisor
Btw, ref_count may also change at any time.
> Is there any > documentation which describes the workflow or code which would use your > new API? >
It's used in the balloon driver (patch 8). We don't have any docs yet, but I think the high level workflow is the two steps above.
Best, Wei
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