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

David Hildenbrand
2024-02-28T10:30:49Z

On 26.02.24 21:55, Zi Yan wrote:
> 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.

Reviewed-by: David Hildenbrand <david@redhat.com>

--
Cheers,

David / dhildenb