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SubjectRe: [patch -mm 1/2] i386: add ptep_test_and_clear_{dirty,young}
David Rientjes wrote:
> On Sun, 25 Mar 2007, Zachary Amsden wrote:
>
>
>> If you actually clear the bit, you need to:
>>
>> + pte_update_defer(vma->vm_mm, addr, ptep);
>>
>> The reason is, when updating PTEs, the hypervisor must be notified. Using
>> atomic operations to do this is fine for all hypervisors I am aware of.
>> However, for hypervisors which shadow page tables, if these PTE modifications
>> are not trapped, you need a post-modification call to fulfill the update of
>> the shadow page table.
>>
>>
>
> Then why was ptep_test_and_clear_{dirty,young} ever removed in the first
> place?? To gain the optimization of one fewer branch and introduce a hack
> to advertise it's existance so the generic header file doesn't include its
> own version?
>

Yes, pretty much.

Zach
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