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    SubjectRe: [PATCH v1 07/11] virtio-mem: Allow to offline partially unplugged memory blocks
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    On 10.03.20 12:43, Michal Hocko wrote:
    > On Mon 02-03-20 14:49:37, David Hildenbrand wrote:
    > [...]
    >> +static void virtio_mem_notify_going_offline(struct virtio_mem *vm,
    >> + unsigned long mb_id)
    >> +{
    >> + const unsigned long nr_pages = PFN_DOWN(vm->subblock_size);
    >> + unsigned long pfn;
    >> + int sb_id, i;
    >> +
    >> + for (sb_id = 0; sb_id < vm->nb_sb_per_mb; sb_id++) {
    >> + if (virtio_mem_mb_test_sb_plugged(vm, mb_id, sb_id, 1))
    >> + continue;
    >> + /*
    >> + * Drop our reference to the pages so the memory can get
    >> + * offlined and add the unplugged pages to the managed
    >> + * page counters (so offlining code can correctly subtract
    >> + * them again).
    >> + */
    >> + pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) +
    >> + sb_id * vm->subblock_size);
    >> + adjust_managed_page_count(pfn_to_page(pfn), nr_pages);
    >> + for (i = 0; i < nr_pages; i++)
    >> + page_ref_dec(pfn_to_page(pfn + i));
    >
    > Is there ever situation this might be a different than 1->0 transition?

    Only if some other code would be taking a reference. At least not from
    virtio-mem perspective.

    --
    Thanks,

    David / dhildenb

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