[PATCH v2 2/9] mm/rmap: refactor hugetlb pte clearing in try_to_unmap_one

Dev Jain
2026-04-10T10:32:39Z

Simplify the code by refactoring the folio_test_hugetlb() branch into
a new function.

No functional change is intended.

Signed-off-by: Dev Jain <dev.jain@arm.com>
---
mm/rmap.c | 116 +++++++++++++++++++++++++++++++-----------------------
1 file changed, 67 insertions(+), 49 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 62a8c912fd788..a9c43e2f6e695 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1978,6 +1978,67 @@ static inline unsigned int folio_unmap_pte_batch(struct folio *folio,
FPB_RESPECT_WRITE | FPB_RESPECT_SOFT_DIRTY);
}

+static inline bool unmap_hugetlb_folio(struct vm_area_struct *vma,
+ struct folio *folio, struct page_vma_mapped_walk *pvmw,
+ struct page *page, enum ttu_flags flags, pte_t *pteval,
+ struct mmu_notifier_range *range, bool *walk_done)
+{
+ /*
+ * The try_to_unmap() is only passed a hugetlb page
+ * in the case where the hugetlb page is poisoned.
+ */
+ VM_WARN_ON_PAGE(!PageHWPoison(page), page);
+ /*
+ * huge_pmd_unshare may unmap an entire PMD page.
+ * There is no way of knowing exactly which PMDs may
+ * be cached for this mm, so we must flush them all.
+ * start/end were already adjusted above to cover this
+ * range.
+ */
+ flush_cache_range(vma, range->start, range->end);
+
+ /*
+ * To call huge_pmd_unshare, i_mmap_rwsem must be
+ * held in write mode. Caller needs to explicitly
+ * do this outside rmap routines.
+ *
+ * We also must hold hugetlb vma_lock in write mode.
+ * Lock order dictates acquiring vma_lock BEFORE
+ * i_mmap_rwsem. We can only try lock here and fail
+ * if unsuccessful.
+ */
+ if (!folio_test_anon(folio)) {
+ struct mmu_gather tlb;
+
+ VM_WARN_ON(!(flags & TTU_RMAP_LOCKED));
+ if (!hugetlb_vma_trylock_write(vma)) {
+ *walk_done = true;
+ return false;
+ }
+
+ tlb_gather_mmu_vma(&tlb, vma);
+ if (huge_pmd_unshare(&tlb, vma, pvmw->address, pvmw->pte)) {
+ hugetlb_vma_unlock_write(vma);
+ huge_pmd_unshare_flush(&tlb, vma);
+ tlb_finish_mmu(&tlb);
+ /*
+ * The PMD table was unmapped,
+ * consequently unmapping the folio.
+ */
+ *walk_done = true;
+ return true;
+ }
+ hugetlb_vma_unlock_write(vma);
+ tlb_finish_mmu(&tlb);
+ }
+ *pteval = huge_ptep_clear_flush(vma, pvmw->address, pvmw->pte);
+ if (pte_dirty(*pteval))
+ folio_mark_dirty(folio);
+
+ *walk_done = false;
+ return true;
+}
+
/*
* @arg: enum ttu_flags will be passed to this argument
*/
@@ -2115,56 +2176,13 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
PageAnonExclusive(subpage);

if (folio_test_hugetlb(folio)) {
- bool anon = folio_test_anon(folio);
-
- /*
- * The try_to_unmap() is only passed a hugetlb page
- * in the case where the hugetlb page is poisoned.
- */
- VM_BUG_ON_PAGE(!PageHWPoison(subpage), subpage);
- /*
- * huge_pmd_unshare may unmap an entire PMD page.
- * There is no way of knowing exactly which PMDs may
- * be cached for this mm, so we must flush them all.
- * start/end were already adjusted above to cover this
- * range.
- */
- flush_cache_range(vma, range.start, range.end);
+ bool walk_done;

- /*
- * To call huge_pmd_unshare, i_mmap_rwsem must be
- * held in write mode. Caller needs to explicitly
- * do this outside rmap routines.
- *
- * We also must hold hugetlb vma_lock in write mode.
- * Lock order dictates acquiring vma_lock BEFORE
- * i_mmap_rwsem. We can only try lock here and fail
- * if unsuccessful.
- */
- if (!anon) {
- struct mmu_gather tlb;
-
- VM_BUG_ON(!(flags & TTU_RMAP_LOCKED));
- if (!hugetlb_vma_trylock_write(vma))
- goto walk_abort;
-
- tlb_gather_mmu_vma(&tlb, vma);
- if (huge_pmd_unshare(&tlb, vma, address, pvmw.pte)) {
- hugetlb_vma_unlock_write(vma);
- huge_pmd_unshare_flush(&tlb, vma);
- tlb_finish_mmu(&tlb);
- /*
- * The PMD table was unmapped,
- * consequently unmapping the folio.
- */
- goto walk_done;
- }
- hugetlb_vma_unlock_write(vma);
- tlb_finish_mmu(&tlb);
- }
- pteval = huge_ptep_clear_flush(vma, address, pvmw.pte);
- if (pte_dirty(pteval))
- folio_mark_dirty(folio);
+ ret = unmap_hugetlb_folio(vma, folio, &pvmw, subpage,
+ flags, &pteval, &range,
+ &walk_done);
+ if (walk_done)
+ goto walk_done;
} else if (likely(pte_present(pteval))) {
nr_pages = folio_unmap_pte_batch(folio, &pvmw, flags, pteval);
end_addr = address + nr_pages * PAGE_SIZE;
--
2.34.1