Let's replicate what we have for PTEs in can_change_pte_writable() also
for PMDs.
While this might look like a pure performance improvement, we'll us this to
get rid of savedwrite handling in do_huge_pmd_numa_page() next. Place
do_huge_pmd_numa_page() strategically good for that purpose.
Note that MM_CP_TRY_CHANGE_WRITABLE is currently only set when we come
via mprotect_fixup().
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
mm/huge_memory.c | 38 ++++++++++++++++++++++++++++++++++++--
1 file changed, 36 insertions(+), 2 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index a524db74e9e6..2ad68e91896a 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1341,6 +1341,36 @@ vm_fault_t do_huge_pmd_wp_page(struct vm_fault *vmf)
return VM_FAULT_FALLBACK;
}
+static inline bool can_change_pmd_writable(struct vm_area_struct *vma,
+ unsigned long addr, pmd_t pmd)
+{
+ struct page *page;
+
+ if (WARN_ON_ONCE(!(vma->vm_flags & VM_WRITE)))
+ return false;
+
+ /* Don't touch entries that are not even readable (NUMA hinting). */
+ if (pmd_protnone(pmd))
+ return false;
+
+ /* Do we need write faults for softdirty tracking? */
+ if (vma_soft_dirty_enabled(vma) && !pmd_soft_dirty(pmd))
+ return false;
+
+ /* Do we need write faults for uffd-wp tracking? */
+ if (userfaultfd_huge_pmd_wp(vma, pmd))
+ return false;
+
+ if (!(vma->vm_flags & VM_SHARED)) {
+ /* See can_change_pte_writable(). */
+ page = vm_normal_page_pmd(vma, addr, pmd);
+ return page && PageAnon(page) && PageAnonExclusive(page);
+ }
+
+ /* See can_change_pte_writable(). */
+ return pmd_dirty(pmd);
+}
+
/* FOLL_FORCE can write to even unwritable PMDs in COW mappings. */
static inline bool can_follow_write_pmd(pmd_t pmd, struct page *page,
struct vm_area_struct *vma,
@@ -1844,13 +1874,17 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
*/
entry = pmd_clear_uffd_wp(entry);
}
+
+ /* See change_pte_range(). */
+ if ((cp_flags & MM_CP_TRY_CHANGE_WRITABLE) && !pmd_write(entry) &&
+ can_change_pmd_writable(vma, addr, entry))
+ entry = pmd_mkwrite(entry);
+
ret = HPAGE_PMD_NR;
set_pmd_at(mm, addr, pmd, entry);
if (huge_pmd_needs_flush(oldpmd, entry))
tlb_flush_pmd_range(tlb, addr, HPAGE_PMD_SIZE);
-
- BUG_ON(vma_is_anonymous(vma) && !preserve_write && pmd_write(entry));
unlock:
spin_unlock(ptl);
return ret;
--
2.38.1
