Re: [RFC 01/11] introduce khugepaged_collapse_single_pmd to collapse a single pmd

[Dev Jain <dev.jain@arm.com>]

On 09/01/25 5:01 am, Nico Pache wrote:
> The khugepaged daemon and madvise_collapse have two different
> implementations that do almost the thing.
> 
> Create khugepaged_collapse_single_pmd to increase code
> reuse and create a entry point for future khugepaged changes.
> 
> Signed-off-by: Nico Pache <npache@redhat.com>
> ---
>   mm/khugepaged.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 46 insertions(+)
> 
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 653dbb1ff05c..4d932839ff1d 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -2348,6 +2348,52 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
>   }
>   #endif
>   
> +/*
> + * Try to collapse a single PMD starting at a PMD aligned addr, and return
> + * the results.
> + */
> +static int khugepaged_collapse_single_pmd(unsigned long addr, struct mm_struct *mm,
> +				   struct vm_area_struct *vma, bool *mmap_locked,
> +				   struct collapse_control *cc)
> +{
> +	int result = SCAN_FAIL;
> +	unsigned long tva_flags = cc->is_khugepaged ? TVA_ENFORCE_SYSFS : 0;
> +
> +	if (!*mmap_locked) {
> +		mmap_read_lock(mm);
> +		*mmap_locked = true;
> +	}
> +
> +	if (thp_vma_allowable_order(vma, vma->vm_flags,
> +					tva_flags, PMD_ORDER)) {
> +		if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) {
> +			struct file *file = get_file(vma->vm_file);
> +			pgoff_t pgoff = linear_page_index(vma, addr);
> +
> +			mmap_read_unlock(mm);
> +			*mmap_locked = false;
> +			result = hpage_collapse_scan_file(mm, addr, file, pgoff,
> +							  cc);
> +			fput(file);
> +			if (result == SCAN_PTE_MAPPED_HUGEPAGE) {
> +				mmap_read_lock(mm);
> +				if (hpage_collapse_test_exit_or_disable(mm))
> +					goto end;
> +				result = collapse_pte_mapped_thp(mm, addr,
> +								 !cc->is_khugepaged);
> +				mmap_read_unlock(mm);
> +			}
> +		} else {
> +			result = hpage_collapse_scan_pmd(mm, vma, addr,
> +							 mmap_locked, cc);
> +		}
> +		if (result == SCAN_SUCCEED || result == SCAN_PMD_MAPPED)
> +			++khugepaged_pages_collapsed;
> +	}
> +end:
> +	return result;
> +}
> +
>   static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
>   					    struct collapse_control *cc)
>   	__releases(&khugepaged_mm_lock)

I will suggest squashing this with patch 2 to avoid unused function 
warning when sequentially building patches.