[PATCH v5 1/8] mm/huge_memory: only split PMD mapping when necessary in unmap_folio()

Zi Yan
2024-02-26T20:56:13Z

From: Zi Yan <ziy@nvidia.com>

As multi-size THP support is added, not all THPs are PMD-mapped, thus
during a huge page split, there is no need to always split PMD mapping
in unmap_folio(). Make it conditional.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
mm/huge_memory.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 28341a5067fb..b20e535e874c 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2727,11 +2727,14 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma,

static void unmap_folio(struct folio *folio)
{
- enum ttu_flags ttu_flags = TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD |
- TTU_SYNC | TTU_BATCH_FLUSH;
+ enum ttu_flags ttu_flags = TTU_RMAP_LOCKED | TTU_SYNC |
+ TTU_BATCH_FLUSH;

VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);

+ if (folio_test_pmd_mappable(folio))
+ ttu_flags |= TTU_SPLIT_HUGE_PMD;
+
/*
* Anon pages need migration entries to preserve them, but file
* pages can simply be left unmapped, then faulted back on demand.
--
2.43.0