[PATCH v2 8/9] mm/huge_memory: deduplicate zap_huge_pmd() further by tracking state

Lorenzo Stoakes (Oracle)
2026-03-19T13:00:47Z

The flush_needed boolean is really tracking whether a PMD entry is present,
so use it that way directly and rename it to is_present.

Deduplicate the folio_remove_rmap_pmd() and folio map count warning between
present and device private by tracking where we need to remove the rmap.

We can also remove the comment about using flush_needed to track whether a
PMD entry is present as it's now irrelevant.

Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
---
mm/huge_memory.c | 28 +++++++++++++---------------
1 file changed, 13 insertions(+), 15 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index c4e00c645e58..22715027e56c 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2430,9 +2430,10 @@ static inline void zap_deposited_table(struct mm_struct *mm, pmd_t *pmd)
bool zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
pmd_t *pmd, unsigned long addr)
{
+ bool needs_remove_rmap = false;
struct folio *folio = NULL;
bool needs_deposit = false;
- bool flush_needed = false;
+ bool is_present = false;
spinlock_t *ptl;
pmd_t orig_pmd;

@@ -2449,6 +2450,7 @@ bool zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
*/
orig_pmd = pmdp_huge_get_and_clear_full(vma, addr, pmd,
tlb->fullmm);
+
arch_check_zapped_pmd(vma, orig_pmd);
tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
if (vma_is_special_huge(vma))
@@ -2458,17 +2460,15 @@ bool zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
goto out;
}

- if (pmd_present(orig_pmd)) {
+ is_present = pmd_present(orig_pmd);
+ if (is_present) {
folio = pmd_folio(orig_pmd);
-
- flush_needed = true;
- folio_remove_rmap_pmd(folio, &folio->page, vma);
- WARN_ON_ONCE(folio_mapcount(folio) < 0);
+ needs_remove_rmap = true;
} else if (pmd_is_valid_softleaf(orig_pmd)) {
const softleaf_t entry = softleaf_from_pmd(orig_pmd);

folio = softleaf_to_folio(entry);
-
+ needs_remove_rmap = folio_is_device_private(folio);
if (!thp_migration_supported())
WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!");
} else {
@@ -2483,27 +2483,25 @@ bool zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
add_mm_counter(tlb->mm, mm_counter_file(folio),
-HPAGE_PMD_NR);

- /*
- * Use flush_needed to indicate whether the PMD entry
- * is present, instead of checking pmd_present() again.
- */
- if (flush_needed && pmd_young(orig_pmd) &&
+ if (is_present && pmd_young(orig_pmd) &&
likely(vma_has_recency(vma)))
folio_mark_accessed(folio);
}

- if (folio_is_device_private(folio)) {
+ if (needs_remove_rmap) {
folio_remove_rmap_pmd(folio, &folio->page, vma);
WARN_ON_ONCE(folio_mapcount(folio) < 0);
- folio_put(folio);
}

out:
if (arch_needs_pgtable_deposit() || needs_deposit)
zap_deposited_table(tlb->mm, pmd);

+ if (needs_remove_rmap && !is_present)
+ folio_put(folio);
+
spin_unlock(ptl);
- if (flush_needed)
+ if (is_present)
tlb_remove_page_size(tlb, &folio->page, HPAGE_PMD_SIZE);
return true;
}
--
2.53.0