From: "Thomas Hellstrom (VMware)" thomas_os@shipmail.org
The functions wp_huge_pmd() and wp_huge_pud() currently relies on the huge_fault() callback to split huge page table entries if needed. However for module users that requires export of the split_huge_xxx() functionality which may be undesired. Instead split pre-existing huge page-table entries on VM_FAULT_FALLBACK return.
We currently only do COW and write-notify on the PTE level, so if the huge_fault() handler returns VM_FAULT_FALLBACK on wp faults, split the huge pages and page-table entries. Also do this for huge PUDs if there is no huge_fault() handler and the vma is not anonymous, similar to how it's done for PMDs.
Note that fs/dax.c still does the splitting in the huge_fault() handler, but as huge_fault() A follow-up patch can remove the dax.c split_huge_pmd() if needed.
Cc: Andrew Morton akpm@linux-foundation.org Cc: Michal Hocko mhocko@suse.com Cc: "Matthew Wilcox (Oracle)" willy@infradead.org Cc: "Kirill A. Shutemov" kirill.shutemov@linux.intel.com Cc: Ralph Campbell rcampbell@nvidia.com Cc: "Jérôme Glisse" jglisse@redhat.com Cc: "Christian König" christian.koenig@amd.com Cc: Dan Williams dan.j.williams@intel.com Signed-off-by: Thomas Hellstrom (VMware) thomas_os@shipmail.org Acked-by: Christian König christian.koenig@amd.com Acked-by: Andrew Morton akpm@linux-foundation.org --- mm/memory.c | 27 +++++++++++++++++++-------- 1 file changed, 19 insertions(+), 8 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c index e8bfdf0d9d1d..efa59b1b109c 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3951,11 +3951,14 @@ static inline vm_fault_t wp_huge_pmd(struct vm_fault *vmf, pmd_t orig_pmd) { if (vma_is_anonymous(vmf->vma)) return do_huge_pmd_wp_page(vmf, orig_pmd); - if (vmf->vma->vm_ops->huge_fault) - return vmf->vma->vm_ops->huge_fault(vmf, PE_SIZE_PMD); + if (vmf->vma->vm_ops->huge_fault) { + vm_fault_t ret = vmf->vma->vm_ops->huge_fault(vmf, PE_SIZE_PMD);
- /* COW handled on pte level: split pmd */ - VM_BUG_ON_VMA(vmf->vma->vm_flags & VM_SHARED, vmf->vma); + if (!(ret & VM_FAULT_FALLBACK)) + return ret; + } + + /* COW or write-notify handled on pte level: split pmd. */ __split_huge_pmd(vmf->vma, vmf->pmd, vmf->address, false, NULL);
return VM_FAULT_FALLBACK; @@ -3968,12 +3971,20 @@ static inline bool vma_is_accessible(struct vm_area_struct *vma)
static vm_fault_t create_huge_pud(struct vm_fault *vmf) { -#ifdef CONFIG_TRANSPARENT_HUGEPAGE +#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && \ + defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD) /* No support for anonymous transparent PUD pages yet */ if (vma_is_anonymous(vmf->vma)) - return VM_FAULT_FALLBACK; - if (vmf->vma->vm_ops->huge_fault) - return vmf->vma->vm_ops->huge_fault(vmf, PE_SIZE_PUD); + goto split; + if (vmf->vma->vm_ops->huge_fault) { + vm_fault_t ret = vmf->vma->vm_ops->huge_fault(vmf, PE_SIZE_PUD); + + if (!(ret & VM_FAULT_FALLBACK)) + return ret; + } +split: + /* COW or write-notify not handled on PUD level: split pud.*/ + __split_huge_pud(vmf->vma, vmf->pud, vmf->address); #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ return VM_FAULT_FALLBACK; }