Re: [PATCH 3/3] KVM: ARM: Transparent huge pages and hugetlbfs support

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?

...

•                   kvm_release_pfn_clean(pfn);
  

•                   pfn &= ~mask;
  

•                   kvm_get_pfn(pfn);
  

•                   *pfnp = pfn;
  

•           }
  

...

•           return true;
  

•   }
  

•   return false;
  

+}

-Christoffer