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SubjectRe: [PATCH 04/11] KVM: page track: add the framework of guest page tracking
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On 12/15/2015 04:46 PM, Xiao Guangrong wrote:
>
>
> On 12/15/2015 03:06 PM, Kai Huang wrote:
>> Hi Guangrong,
>>
>> I am starting to review this series, and should have some comments or
>> questions, you can determine
>> whether they are valuable :)
>
> Thank you very much for your review and breaking the silent on this
> patchset. ;)
>
>
>>> +static void page_track_slot_free(struct kvm_memory_slot *slot)
>>> +{
>>> + int i;
>>> +
>>> + for (i = 0; i < KVM_PAGE_TRACK_MAX; i++)
>>> + if (slot->arch.gfn_track[i]) {
>>> + kvfree(slot->arch.gfn_track[i]);
>>> + slot->arch.gfn_track[i] = NULL;
>>> + }
>>> +}
>>> +
>>> +int kvm_page_track_create_memslot(struct kvm_memory_slot *slot,
>>> + unsigned long npages)
>>> +{
>>> + int i, pages = gfn_to_index(slot->base_gfn + npages - 1,
>>> + slot->base_gfn, PT_PAGE_TABLE_LEVEL) + 1;
>>> +
>>> + for (i = 0; i < KVM_PAGE_TRACK_MAX; i++) {
>>> + slot->arch.gfn_track[i] = kvm_kvzalloc(pages *
>>> + sizeof(*slot->arch.gfn_track[i]));
>>> + if (!slot->arch.gfn_track[i])
>>> + goto track_free;
>>> + }
>>> +
>>> + return 0;
>>> +
>>> +track_free:
>>> + page_track_slot_free(slot);
>>> + return -ENOMEM;
>>> +}
>> Is it necessary to use the 'unsigned long npages' pareameter? In my
>> understanding you are going to
>
> The type, 'int', is used here as I followed the style of 'struct
> kvm_lpage_info'.
>
> 4 bytes should be enough to track all users and signed type is good to
> track
> overflow.
>
>> track all GFNs in the memory slot anyway, right? If you want to keep
>> npages, I think it's better to
>> add a base_gfn as well otherwise you are assuming you are going to
>> track the npages GFN starting
>> from slot->base_gfn.
>
> Yes, any page in the memslot may be tracked so that there is a index
> for every
> page.
>
>>
>>> +
>>> +void kvm_page_track_free_memslot(struct kvm_memory_slot *free,
>>> + struct kvm_memory_slot *dont)
>>> +{
>>> + if (!dont || free->arch.gfn_track != dont->arch.gfn_track)
>>> + page_track_slot_free(free);
>>> +}
>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>>> index c04987e..ad4888a 100644
>>> --- a/arch/x86/kvm/x86.c
>>> +++ b/arch/x86/kvm/x86.c
>>> @@ -7838,6 +7838,8 @@ void kvm_arch_free_memslot(struct kvm *kvm,
>>> struct kvm_memory_slot *free,
>>> free->arch.lpage_info[i - 1] = NULL;
>>> }
>>> }
>>> +
>>> + kvm_page_track_free_memslot(free, dont);
>>> }
>>> int kvm_arch_create_memslot(struct kvm *kvm, struct
>>> kvm_memory_slot *slot,
>>> @@ -7886,6 +7888,9 @@ int kvm_arch_create_memslot(struct kvm *kvm,
>>> struct kvm_memory_slot *slot,
>>> }
>>> }
>>> + if (kvm_page_track_create_memslot(slot, npages))
>>> + goto out_free;
>>> +
>> Looks essentially you are allocating one int for all GFNs of the slot
>> unconditionally. In my
>> understanding for most of memory slots, we are not going to track
>> them, so isn't it going to be
>> wasteful of memory?
>>
>
> Yes, hmm... maybe we can make the index as "unsigned short" then 1G
> memory only needs 512k index
> buffer. It is not so unacceptable.
Those comments are really minor and don't bother on this :)

Thanks,
-Kai



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