[PATCH v1 11/11] mm/ksm: convert break_ksm() from walk_page_range_vma() to folio_walk

David Hildenbrand
2024-08-02T15:56:53Z

Let's simplify by reusing folio_walk. Keep the existing behavior by
handling migration entries and zeropages.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
mm/ksm.c | 63 ++++++++++++++------------------------------------------
1 file changed, 16 insertions(+), 47 deletions(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index 0f5b2bba4ef0..8e53666bc7b0 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -608,47 +608,6 @@ static inline bool ksm_test_exit(struct mm_struct *mm)
return atomic_read(&mm->mm_users) == 0;
}

-static int break_ksm_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long next,
- struct mm_walk *walk)
-{
- struct page *page = NULL;
- spinlock_t *ptl;
- pte_t *pte;
- pte_t ptent;
- int ret;
-
- pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
- if (!pte)
- return 0;
- ptent = ptep_get(pte);
- if (pte_present(ptent)) {
- page = vm_normal_page(walk->vma, addr, ptent);
- } else if (!pte_none(ptent)) {
- swp_entry_t entry = pte_to_swp_entry(ptent);
-
- /*
- * As KSM pages remain KSM pages until freed, no need to wait
- * here for migration to end.
- */
- if (is_migration_entry(entry))
- page = pfn_swap_entry_to_page(entry);
- }
- /* return 1 if the page is an normal ksm page or KSM-placed zero page */
- ret = (page && PageKsm(page)) || is_ksm_zero_pte(ptent);
- pte_unmap_unlock(pte, ptl);
- return ret;
-}
-
-static const struct mm_walk_ops break_ksm_ops = {
- .pmd_entry = break_ksm_pmd_entry,
- .walk_lock = PGWALK_RDLOCK,
-};
-
-static const struct mm_walk_ops break_ksm_lock_vma_ops = {
- .pmd_entry = break_ksm_pmd_entry,
- .walk_lock = PGWALK_WRLOCK,
-};
-
/*
* We use break_ksm to break COW on a ksm page by triggering unsharing,
* such that the ksm page will get replaced by an exclusive anonymous page.
@@ -665,16 +624,26 @@ static const struct mm_walk_ops break_ksm_lock_vma_ops = {
static int break_ksm(struct vm_area_struct *vma, unsigned long addr, bool lock_vma)
{
vm_fault_t ret = 0;
- const struct mm_walk_ops *ops = lock_vma ?
- &break_ksm_lock_vma_ops : &break_ksm_ops;
+
+ if (lock_vma)
+ vma_start_write(vma);

do {
- int ksm_page;
+ bool ksm_page = false;
+ struct folio_walk fw;
+ struct folio *folio;

cond_resched();
- ksm_page = walk_page_range_vma(vma, addr, addr + 1, ops, NULL);
- if (WARN_ON_ONCE(ksm_page < 0))
- return ksm_page;
+ folio = folio_walk_start(&fw, vma, addr,
+ FW_MIGRATION | FW_ZEROPAGE);
+ if (folio) {
+ /* Small folio implies FW_LEVEL_PTE. */
+ if (!folio_test_large(folio) &&
+ (folio_test_ksm(folio) || is_ksm_zero_pte(fw.pte)))
+ ksm_page = true;
+ folio_walk_end(&fw, vma);
+ }
+
if (!ksm_page)
return 0;
ret = handle_mm_fault(vma, addr,
--
2.45.2