Re: [RFC PATCH v2 04/11] mm: khugepaged: add shmem mTHP collapse support

[Lance Yang <lance.yang@linux.dev>]

On Wed, Jun 10, 2026 at 06:29:12PM +0800, Baolin Wang wrote:
[...]
>@@ -2768,15 +2827,23 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm,
> 	else
> 		cc->progress += HPAGE_PMD_NR;
> 
>-	if (result == SCAN_SUCCEED) {
>-		if (present < HPAGE_PMD_NR - max_ptes_none) {
>-			result = SCAN_EXCEED_NONE_PTE;
>-			count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
>-		} else {
>-			result = collapse_file(mm, addr, file, start, cc, HPAGE_PMD_ORDER);
>-		}
>+	if (result != SCAN_SUCCEED)
>+		goto out;
>+
>+	if (present < HPAGE_PMD_NR - max_ptes_none) {
>+		result = SCAN_EXCEED_NONE_PTE;
>+		count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
>+		count_mthp_stat(HPAGE_PMD_ORDER,
>+				MTHP_STAT_COLLAPSE_EXCEED_NONE);
>+		goto out;
> 	}
> 
>+	result = mthp_collapse(mm, file, start, addr, 0, 0, cc, enabled_orders);

Feels like the second 0 wants to be "swap", no?

>+	if (result == SCAN_SUCCEED && !cc->is_khugepaged) {
>+		/* If MADV_COLLAPSE, adjust result to call collapse_pte_mapped_thp(). */
>+		result = SCAN_PTE_MAPPED_HUGEPAGE;
>+	}
>+out:
> 	trace_mm_khugepaged_scan_file(mm, folio, file, present, swap, result);
> 	return result;
> }
>@@ -2808,7 +2875,7 @@ static enum scan_result collapse_single_pmd(unsigned long addr,
> 	mmap_read_unlock(mm);
> 	*lock_dropped = true;
> retry:
>-	result = collapse_scan_file(mm, addr, file, pgoff, cc);
>+	result = collapse_scan_file(mm, vma, addr, file, pgoff, cc);
> 
> 	/*
> 	 * For MADV_COLLAPSE, when encountering dirty pages, try to writeback,
>-- 
>2.47.3
>
>