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

[David Hildenbrand <david@redhat.com>]

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