On 2013-10-03 21:33, Christoffer Dall wrote:
> On Mon, Sep 23, 2013 at 11:11:07AM +0100, Marc Zyngier wrote:
>
> [...]
>
>> >
>> > +static bool transparent_hugepage_adjust(pfn_t *pfnp, phys_addr_t
>> *ipap)
>> > +{
>> > + pfn_t pfn = *pfnp;
>> > + gfn_t gfn = *ipap >> PAGE_SHIFT;
>> > +
>> > + if (PageTransCompound(pfn_to_page(pfn))) {
>> > + unsigned long mask;
>> > + /*
>> > + * mmu_notifier_retry was successful and we hold
>> the
>> > + * mmu_lock here, so the pmd can't become
>> splitting
>> > + * from under us, and in turn
>> > + * __split_huge_page_refcount() can't run from
>> under
>> > + * us and we can safely transfer the refcount from
>> > + * PG_tail to PG_head as we switch the pfn from
>> tail to
>> > + * head.
>> > + */
>>
>> -ECANTPARSE. Well, I sort of can, but this deserves a clearer
>> explanation.
>>
>> > + mask = (PMD_SIZE / PAGE_SIZE) - 1;
>>
>> mask = PTRS_PER_PMD -1;
>>
>> > + VM_BUG_ON((gfn & mask) != (pfn & mask));
>> > + if (pfn & mask) {
>> > + gfn &= ~mask;
>>
>> This doesn't seem to be used later on.
>>
>> > + *ipap &= ~(PMD_SIZE - 1);
>>
>> *ipap &= ~PMD_MASK;
>>
> damn, I trust you too much, you surely meant
> *ipap &= PMD_MASK;
>
> right?
Indeed. Just keeping you on your toes ;-)
M.
--
Fast, cheap, reliable. Pick two.
_______________________________________________
kvmarm mailing list
kvmarm@xxxxxxxxxxxxxxxxxxxxx
https://lists.cs.columbia.edu/cucslists/listinfo/kvmarm
