Re: [PATCH] arm64/hugetlb: Implement arm64 specific hugetlb_mask_last_hp

[Baoquan He]

On 06/16/22 at 11:34am, Baolin Wang wrote:
> The HugeTLB address ranges are linearly scanned during fork, unmap and
> remap operations, and the linear scan can skip to the end of range mapped
> by the page table page if hitting a non-present entry, which can help
> to speed linear scanning of the HugeTLB address ranges.
> 
> So hugetlb_mask_last_hp() is introduced to help to update the address in
> the loop of HugeTLB linear scanning with getting the last huge page mapped
> by the associated page table page[1], when a non-present entry is encountered.
> 
> Considering ARM64 specific cont-pte/pmd size HugeTLB, this patch implemented
> an ARM64 specific hugetlb_mask_last_hp() to help this case.
> 
> [1] https://lore.kernel.org/linux-mm/20220527225849.284839-1-mike.kravetz@xxxxxxxxxx/
> 
> Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> ---
> Note: this patch is based on the series: "hugetlb: speed up linear
> address scanning" from Mike. Mike, please fold it into your series.
> Thanks.
> ---
>  arch/arm64/mm/hugetlbpage.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
> index e2a5ec9..958935c 100644
> --- a/arch/arm64/mm/hugetlbpage.c
> +++ b/arch/arm64/mm/hugetlbpage.c
> @@ -368,6 +368,26 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
>  	return NULL;
>  }
>  
> +unsigned long hugetlb_mask_last_hp(struct hstate *h)
> +{
> +	unsigned long hp_size = huge_page_size(h);

hp_size may not be a good name, it reminds me of hotplug. I would name
it hpage_size even though a little more characters are added.

> +
> +	switch (hp_size) {
> +	case PUD_SIZE:
> +		return PGDIR_SIZE - PUD_SIZE;
> +	case CONT_PMD_SIZE:
> +		return PUD_SIZE - CONT_PMD_SIZE;
> +	case PMD_SIZE:
> +		return PUD_SIZE - PMD_SIZE;
> +	case CONT_PTE_SIZE:
> +		return PMD_SIZE - CONT_PTE_SIZE;
> +	default:
> +		break;
> +	}
> +
> +	return ~0UL;
> +}
> +
>  pte_t arch_make_huge_pte(pte_t entry, unsigned int shift, vm_flags_t flags)
>  {
>  	size_t pagesize = 1UL << shift;
> -- 
> 1.8.3.1
> 
>