linux-kernel - Re: [PATCH v2 1/2] mm: Make pte_range_none() return number of empty PTEs

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Message-ID: <CAGsJ_4xeNLd9xrQ531xqpKkpwPSsWF_44rzftvMbFAD0-X3ZQg@mail.gmail.com>
Date: Thu, 19 Sep 2024 13:38:00 +1200
From: Barry Song <baohua@...nel.org>
To: Dev Jain <dev.jain@....com>
Cc: akpm@...ux-foundation.org, david@...hat.com, willy@...radead.org, 
	ryan.roberts@....com, anshuman.khandual@....com, hughd@...gle.com, 
	ioworker0@...il.com, wangkefeng.wang@...wei.com, 
	baolin.wang@...ux.alibaba.com, gshan@...hat.com, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org
Subject: Re: [PATCH v2 1/2] mm: Make pte_range_none() return number of empty PTEs

On Mon, Sep 16, 2024 at 11:08 PM Dev Jain <dev.jain@....com> wrote:
>
> In preparation for the second patch, make pte_range_none() return
> the number of contiguous empty PTEs.
>
> Signed-off-by: Dev Jain <dev.jain@....com>
> ---
>  mm/memory.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 6469ac99f2f7..8bb1236de93c 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4617,16 +4617,16 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>         return ret;
>  }
>
> -static bool pte_range_none(pte_t *pte, int nr_pages)
> +static int pte_range_none(pte_t *pte, int nr_pages)
>  {
>         int i;
>
>         for (i = 0; i < nr_pages; i++) {
>                 if (!pte_none(ptep_get_lockless(pte + i)))
> -                       return false;
> +                       return i;
>         }
>
> -       return true;
> +       return nr_pages;
>  }
>
>  static struct folio *alloc_anon_folio(struct vm_fault *vmf)
> @@ -4671,7 +4671,7 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf)
>         order = highest_order(orders);
>         while (orders) {
>                 addr = ALIGN_DOWN(vmf->address, PAGE_SIZE << order);
> -               if (pte_range_none(pte + pte_index(addr), 1 << order))
> +               if (pte_range_none(pte + pte_index(addr), 1 << order) == 1 << order)

Minor suggestion: it's a bit odd that we're doing 1 << order twice.
Perhaps consider
introducing a local variable, nr_pages, for clarity.

Otherwise,

Reviewed-by: Barry Song <baohua@...nel.org>


>                         break;
>                 order = next_order(&orders, order);
>         }
> @@ -4787,7 +4787,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
>         if (nr_pages == 1 && vmf_pte_changed(vmf)) {
>                 update_mmu_tlb(vma, addr, vmf->pte);
>                 goto release;
> -       } else if (nr_pages > 1 && !pte_range_none(vmf->pte, nr_pages)) {
> +       } else if (nr_pages > 1 && pte_range_none(vmf->pte, nr_pages) != nr_pages) {
>                 update_mmu_tlb_range(vma, addr, vmf->pte, nr_pages);
>                 goto release;
>         }
> @@ -5121,7 +5121,7 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
>                 update_mmu_tlb(vma, addr, vmf->pte);
>                 ret = VM_FAULT_NOPAGE;
>                 goto unlock;
> -       } else if (nr_pages > 1 && !pte_range_none(vmf->pte, nr_pages)) {
> +       } else if (nr_pages > 1 && pte_range_none(vmf->pte, nr_pages) != nr_pages) {
>                 update_mmu_tlb_range(vma, addr, vmf->pte, nr_pages);
>                 ret = VM_FAULT_NOPAGE;
>                 goto unlock;
> --
> 2.30.2
>

Thanks
Barry