[PATCH v1 07/14] mm/pagewalk.c: add pud_entry_post() for post-order traversals

[Yu Zhao]

Add a new callback pud_entry_post() to struct mm_walk_ops so that page
table walkers can visit the non-leaf PMD entries of a PUD entry after
they have visited with the leaf PTE entries. This allows page table
walkers who clear the accessed bit to take advantage of the last
commit, in a similar way walk_pte_range() works for the PTE entries of
a PMD entry: they only need to take PTL once to search all the child
entries of a parent entry.

Signed-off-by: Yu Zhao <yuz...@google.com>
---
 include/linux/pagewalk.h | 4 ++++
 mm/pagewalk.c            | 5 +++++
 2 files changed, 9 insertions(+)

diff --git a/include/linux/pagewalk.h b/include/linux/pagewalk.h
index b1cb6b753abb..2b68ae9d27d3 100644
--- a/include/linux/pagewalk.h
+++ b/include/linux/pagewalk.h
@@ -11,6 +11,8 @@ struct mm_walk;
  * @pgd_entry:         if set, called for each non-empty PGD (top-level) entry
  * @p4d_entry:         if set, called for each non-empty P4D entry
  * @pud_entry:         if set, called for each non-empty PUD entry
+ * @pud_entry_post:    if set, called for each non-empty PUD entry after
+ *                     pmd_entry is called, for post-order traversal.
  * @pmd_entry:         if set, called for each non-empty PMD entry
  *                     this handler is required to be able to handle
  *                     pmd_trans_huge() pmds.  They may simply choose to
@@ -41,6 +43,8 @@ struct mm_walk_ops {
                         unsigned long next, struct mm_walk *walk);
        int (*pud_entry)(pud_t *pud, unsigned long addr,
                         unsigned long next, struct mm_walk *walk);
+       int (*pud_entry_post)(pud_t *pud, unsigned long addr,
+                             unsigned long next, struct mm_walk *walk);
        int (*pmd_entry)(pmd_t *pmd, unsigned long addr,
                         unsigned long next, struct mm_walk *walk);
        int (*pte_entry)(pte_t *pte, unsigned long addr,
diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index e81640d9f177..8ed1533f7eda 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -160,6 +160,11 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, 
unsigned long end,
                err = walk_pmd_range(pud, addr, next, walk);
                if (err)
                        break;
+
+               if (ops->pud_entry_post)
+                       err = ops->pud_entry_post(pud, addr, next, walk);
+               if (err)
+                       break;
        } while (pud++, addr = next, addr != end);
 
        return err;
-- 
2.31.0.rc2.261.g7f71774620-goog