[PATCH v5 2/9] mm: Introduce vma_is_special_huge

Thomas Hellström (VMware)
2020-03-03T10:23:23Z

For VM_PFNMAP and VM_MIXEDMAP vmas that want to support transhuge pages
and -page table entries, introduce vma_is_special_huge() that takes the
same codepaths as vma_is_dax().

The use of "special" follows the definition in memory.c, vm_normal_page():
"Special" mappings do not wish to be associated with a "struct page"
(either it doesn't exist, or it exists but they don't want to touch it)

For PAGE_SIZE pages, "special" is determined per page table entry to be
able to deal with COW pages. But since we don't have huge COW pages,
we can classify a vma as either "special huge" or "normal huge".

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 <thellstrom@vmware.com>
Acked-by: Christian König <christian.koenig@amd.com>
---
include/linux/mm.h | 17 +++++++++++++++++
mm/huge_memory.c | 6 +++---
2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 52269e56c514..e61cf3f609b4 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2863,6 +2863,23 @@ extern long copy_huge_page_from_user(struct page *dst_page,
const void __user *usr_src,
unsigned int pages_per_huge_page,
bool allow_pagefault);
+
+/**
+ * vma_is_special_huge - Are transhuge page-table entries considered special?
+ * @vma: Pointer to the struct vm_area_struct to consider
+ *
+ * Whether transhuge page-table entries are considered "special" following
+ * the definition in vm_normal_page().
+ *
+ * Return: true if transhuge page-table entries should be considered special,
+ * false otherwise.
+ */
+static inline bool vma_is_special_huge(const struct vm_area_struct *vma)
+{
+ return vma_is_dax(vma) || (vma->vm_file &&
+ (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP)));
+}
+
#endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */

#ifdef CONFIG_DEBUG_PAGEALLOC
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index b08b199f9a11..ff7a8b85c3ba 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1802,7 +1802,7 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
orig_pmd = pmdp_huge_get_and_clear_full(tlb->mm, addr, pmd,
tlb->fullmm);
tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
- if (vma_is_dax(vma)) {
+ if (vma_is_special_huge(vma)) {
if (arch_needs_pgtable_deposit())
zap_deposited_table(tlb->mm, pmd);
spin_unlock(ptl);
@@ -2066,7 +2066,7 @@ int zap_huge_pud(struct mmu_gather *tlb, struct vm_area_struct *vma,
*/
pudp_huge_get_and_clear_full(tlb->mm, addr, pud, tlb->fullmm);
tlb_remove_pud_tlb_entry(tlb, pud, addr);
- if (vma_is_dax(vma)) {
+ if (vma_is_special_huge(vma)) {
spin_unlock(ptl);
/* No zero page support yet */
} else {
@@ -2175,7 +2175,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
*/
if (arch_needs_pgtable_deposit())
zap_deposited_table(mm, pmd);
- if (vma_is_dax(vma))
+ if (vma_is_special_huge(vma))
return;
page = pmd_page(_pmd);
if (!PageDirty(page) && pmd_dirty(_pmd))
--
2.21.1