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

Dev Jain
2025-01-10T06:25:32Z

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.