Messages in this thread | | | Date | Wed, 26 Jul 2017 10:22:23 +0800 | From | Wei Wang <> | Subject | Re: [PATCH v12 6/8] mm: support reporting free page blocks |
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On 07/25/2017 10:53 PM, Michal Hocko wrote: > On Tue 25-07-17 14:47:16, Wang, Wei W wrote: >> On Tuesday, July 25, 2017 8:42 PM, hal Hocko wrote: >>> On Tue 25-07-17 19:56:24, Wei Wang wrote: >>>> On 07/25/2017 07:25 PM, Michal Hocko wrote: >>>>> On Tue 25-07-17 17:32:00, Wei Wang wrote: >>>>>> 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: >>>>>>> [... >>>> We don't need to do the pfn walk in the guest kernel. When the API >>>> reports, for example, a 2MB free page block, the API caller offers to >>>> the hypervisor the base address of the page block, and size=2MB, to >>>> the hypervisor. >>> So you want to skip pfn walks by regularly calling into the page allocator to >>> update your bitmap. If that is the case then would an API that would allow you >>> to update your bitmap via a callback be s sufficient? Something like >>> void walk_free_mem(int node, int min_order, >>> void (*visit)(unsigned long pfn, unsigned long nr_pages)) >>> >>> The function will call the given callback for each free memory block on the given >>> node starting from the given min_order. The callback will be strictly an atomic >>> and very light context. You can update your bitmap from there. >> I would need to introduce more about the background here: >> The hypervisor and the guest live in their own address space. The hypervisor's bitmap >> isn't seen by the guest. I think we also wouldn't be able to give a callback function >> from the hypervisor to the guest in this case. > How did you plan to use your original API which export struct page array > then?
That's where the virtio-balloon driver comes in. It uses a shared ring mechanism to send the guest memory info to the hypervisor.
We didn't expose the struct page array from the guest to the hypervisor. For example, when a 2MB free page block is reported from the free page list, the info put on the ring is just (base address of the 2MB continuous memory, size=2M).
> >>> This would address my main concern that the allocator internals would get >>> outside of the allocator proper. >> What issue would it have to expose the internal, for_each_zone()? > zone is a MM internal concept. No code outside of the MM proper should > really care about zones.
I think this is also what Andrew suggested in the previous discussion: https://lkml.org/lkml/2017/3/16/951
Move the code to virtio-balloon and a little layering violation seems acceptable.
Best, Wei
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