| Message ID | 20230928173205.2826598-2-vdonnefort@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: arm64: Use folio for THP support | expand |
On 9/29/23 03:32, Vincent Donnefort wrote: > GUP affects a refcount common to all pages forming the THP. There is > therefore no need to move the refcount from a tail to the head page. > Under the hood it decrements and increments the same counter. > > Signed-off-by: Vincent Donnefort <vdonnefort@google.com> > Reviewed-by: Gavin Shan <gshan@redhat.com> > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index 587a104f66c3..de5e5148ef5d 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -1295,28 +1295,8 @@ transparent_hugepage_adjust(struct kvm *kvm, struct kvm_memory_slot *memslot, > if (sz < PMD_SIZE) > return PAGE_SIZE; > > - /* > - * The address we faulted on is backed by a transparent huge > - * page. However, because we map the compound huge page and > - * not the individual tail page, we need to transfer the > - * refcount to the head page. We have to be careful that the > - * THP doesn't start to split while we are adjusting the > - * refcounts. > - * > - * We are sure this doesn't happen, because mmu_invalidate_retry > - * was successful and we are holding the mmu_lock, so if this > - * THP is trying to split, it will be blocked in the mmu > - * notifier before touching any of the pages, specifically > - * before being able to call __split_huge_page_refcount(). > - * > - * We can therefore safely transfer the refcount from PG_tail > - * to PG_head and switch the pfn from a tail page to the head > - * page accordingly. > - */ > *ipap &= PMD_MASK; > - kvm_release_pfn_clean(pfn); > pfn &= ~(PTRS_PER_PMD - 1); > - get_page(pfn_to_page(pfn)); > *pfnp = pfn; > > return PMD_SIZE; The local variable @pfn can be dropped either. *pfnp &= ~(PTRS_PER_PMD - 1); Thanks, Gavin
On Fri, Sep 29, 2023 at 04:59:20PM +1000, Gavin Shan wrote: > On 9/29/23 03:32, Vincent Donnefort wrote: > > GUP affects a refcount common to all pages forming the THP. There is > > therefore no need to move the refcount from a tail to the head page. > > Under the hood it decrements and increments the same counter. > > > > Signed-off-by: Vincent Donnefort <vdonnefort@google.com> > > > > Reviewed-by: Gavin Shan <gshan@redhat.com> > > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > > index 587a104f66c3..de5e5148ef5d 100644 > > --- a/arch/arm64/kvm/mmu.c > > +++ b/arch/arm64/kvm/mmu.c > > @@ -1295,28 +1295,8 @@ transparent_hugepage_adjust(struct kvm *kvm, struct kvm_memory_slot *memslot, > > if (sz < PMD_SIZE) > > return PAGE_SIZE; > > - /* > > - * The address we faulted on is backed by a transparent huge > > - * page. However, because we map the compound huge page and > > - * not the individual tail page, we need to transfer the > > - * refcount to the head page. We have to be careful that the > > - * THP doesn't start to split while we are adjusting the > > - * refcounts. > > - * > > - * We are sure this doesn't happen, because mmu_invalidate_retry > > - * was successful and we are holding the mmu_lock, so if this > > - * THP is trying to split, it will be blocked in the mmu > > - * notifier before touching any of the pages, specifically > > - * before being able to call __split_huge_page_refcount(). > > - * > > - * We can therefore safely transfer the refcount from PG_tail > > - * to PG_head and switch the pfn from a tail page to the head > > - * page accordingly. > > - */ > > *ipap &= PMD_MASK; > > - kvm_release_pfn_clean(pfn); > > pfn &= ~(PTRS_PER_PMD - 1); > > - get_page(pfn_to_page(pfn)); > > *pfnp = pfn; > > return PMD_SIZE; > > The local variable @pfn can be dropped either. I would like to keep it for the following patch: pfn_to_folio(pfn); > > *pfnp &= ~(PTRS_PER_PMD - 1); > > Thanks, > Gavin >
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c index 587a104f66c3..de5e5148ef5d 100644 --- a/arch/arm64/kvm/mmu.c +++ b/arch/arm64/kvm/mmu.c @@ -1295,28 +1295,8 @@ transparent_hugepage_adjust(struct kvm *kvm, struct kvm_memory_slot *memslot, if (sz < PMD_SIZE) return PAGE_SIZE; - /* - * The address we faulted on is backed by a transparent huge - * page. However, because we map the compound huge page and - * not the individual tail page, we need to transfer the - * refcount to the head page. We have to be careful that the - * THP doesn't start to split while we are adjusting the - * refcounts. - * - * We are sure this doesn't happen, because mmu_invalidate_retry - * was successful and we are holding the mmu_lock, so if this - * THP is trying to split, it will be blocked in the mmu - * notifier before touching any of the pages, specifically - * before being able to call __split_huge_page_refcount(). - * - * We can therefore safely transfer the refcount from PG_tail - * to PG_head and switch the pfn from a tail page to the head - * page accordingly. - */ *ipap &= PMD_MASK; - kvm_release_pfn_clean(pfn); pfn &= ~(PTRS_PER_PMD - 1); - get_page(pfn_to_page(pfn)); *pfnp = pfn; return PMD_SIZE;
GUP affects a refcount common to all pages forming the THP. There is therefore no need to move the refcount from a tail to the head page. Under the hood it decrements and increments the same counter. Signed-off-by: Vincent Donnefort <vdonnefort@google.com>