Re: [PATCH v3 05/13] mm/huge_memory: add a common exit path to zap_huge_pmd()

[Suren Baghdasaryan <surenb@google.com>]

On Fri, Mar 20, 2026 at 11:07 AM Lorenzo Stoakes (Oracle)
<ljs@kernel.org> wrote:
>
> Other than when we acquire the PTL, we always need to unlock the PTL, and
> optionally need to flush on exit.
>
> The code is currently very duplicated in this respect, so default
> flush_needed to false, set it true in the case in which it's required,
> then share the same logic for all exit paths.
>
> This also makes flush_needed make more sense as a function-scope value (we
> don't need to flush for the PFN map/mixed map, zero huge, error cases for
> instance).
>
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>

Reviewed-by: Suren Baghdasaryan <surenb@google.com>

> ---
>  mm/huge_memory.c | 15 ++++++---------
>  1 file changed, 6 insertions(+), 9 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 0056ac27ec9a..b9d9acfef147 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2338,7 +2338,7 @@ bool zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
>                  pmd_t *pmd, unsigned long addr)
>  {
>         struct folio *folio = NULL;
> -       bool flush_needed = true;
> +       bool flush_needed = false;
>         spinlock_t *ptl;
>         pmd_t orig_pmd;
>
> @@ -2360,19 +2360,18 @@ bool zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
>         if (vma_is_special_huge(vma)) {
>                 if (arch_needs_pgtable_deposit())
>                         zap_deposited_table(tlb->mm, pmd);
> -               spin_unlock(ptl);
> -               return true;
> +               goto out;
>         }
>         if (is_huge_zero_pmd(orig_pmd)) {
>                 if (!vma_is_dax(vma) || arch_needs_pgtable_deposit())
>                         zap_deposited_table(tlb->mm, pmd);
> -               spin_unlock(ptl);
> -               return true;
> +               goto out;
>         }
>
>         if (pmd_present(orig_pmd)) {
>                 struct page *page = pmd_page(orig_pmd);
>
> +               flush_needed = true;
>                 folio = page_folio(page);
>                 folio_remove_rmap_pmd(folio, page, vma);
>                 WARN_ON_ONCE(folio_mapcount(folio) < 0);
> @@ -2381,14 +2380,12 @@ bool zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
>                 const softleaf_t entry = softleaf_from_pmd(orig_pmd);
>
>                 folio = softleaf_to_folio(entry);
> -               flush_needed = false;
>
>                 if (!thp_migration_supported())
>                         WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!");
>         } else {
>                 WARN_ON_ONCE(true);
> -               spin_unlock(ptl);
> -               return true;
> +               goto out;
>         }
>
>         if (folio_test_anon(folio)) {
> @@ -2415,10 +2412,10 @@ bool zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
>                 folio_put(folio);
>         }
>
> +out:
>         spin_unlock(ptl);
>         if (flush_needed)
>                 tlb_remove_page_size(tlb, &folio->page, HPAGE_PMD_SIZE);
> -
>         return true;
>  }
>
> --
> 2.53.0
>