Messages in this thread | | | Date | Wed, 26 Jul 2017 19:44:23 +0800 | From | Wei Wang <> | Subject | Re: [PATCH v12 6/8] mm: support reporting free page blocks |
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On 07/26/2017 06:24 PM, Michal Hocko wrote: > On Wed 26-07-17 10:22:23, Wei Wang wrote: >> 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). > So what exactly prevents virtio-balloon from using the above proposed > callback mechanism and export what is needed to the hypervisor?
I thought about it more. Probably we can use the callback function with a little change like this:
void walk_free_mem(void *opaque1, void (*visit)(void *opaque2, unsigned long pfn, unsigned long nr_pages)) { ... for_each_populated_zone(zone) { for_each_migratetype_order(order, type) { report_unused_page_block(zone, order, type, &page); // from patch 6 pfn = page_to_pfn(page); visit(opaque1, pfn, 1 << order); } } }
The above function scans all the free list and directly sends each free page block to the hypervisor via the virtio_balloon callback below. No need to implement a bitmap.
In virtio-balloon, we have the callback: void *virtio_balloon_report_unused_pages(void *opaque, unsigned long pfn, unsigned long nr_pages) { struct virtio_balloon *vb = (struct virtio_balloon *)opaque; ...put the free page block to the the ring of vb; }
What do you think?
Best, Wei
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