[PATCH 04/10] mm: allow a NULL fn callback in apply_to_page_range

[Christoph Hellwig <hch@xxxxxx>]

Besides calling the callback on each page, apply_to_page_range also has
the effect of pre-faulting all PTEs for the range.  To support callers
that only need the pre-faulting, make the callback optional.

Based on a patch from Minchan Kim <minchan@xxxxxxxxxx>.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
 mm/memory.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index fcfc4ca36eba80..dcf2bb69fbf847 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2420,13 +2420,15 @@ static int apply_to_pte_range(struct mm_struct *mm, 
pmd_t *pmd,
 
        arch_enter_lazy_mmu_mode();
 
-       do {
-               if (create || !pte_none(*pte)) {
-                       err = fn(pte++, addr, data);
-                       if (err)
-                               break;
-               }
-       } while (addr += PAGE_SIZE, addr != end);
+       if (fn) {
+               do {
+                       if (create || !pte_none(*pte)) {
+                               err = fn(pte++, addr, data);
+                               if (err)
+                                       break;
+                       }
+               } while (addr += PAGE_SIZE, addr != end);
+       }
        *mask |= PGTBL_PTE_MODIFIED;
 
        arch_leave_lazy_mmu_mode();
-- 
2.28.0