mm: Split huge pages on write-notify or COW (327e9fd4) · Commits · 戴 / test

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

+19 −8

Original line number	Diff line number	Diff line
		@@ -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;
		}

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