Re: [PATCH 1/3] mm/khugepaged: remove unnecessary goto 'skip' label

On 12/20/2025 6:08 AM, Wei Yang wrote:

On Fri, Dec 19, 2025 at 02:54:40PM +0530, Garg, Shivank wrote:

quoted

On 12/17/2025 8:18 AM, Wei Yang wrote:

quoted

On Tue, Dec 16, 2025 at 11:11:38AM +0000, Shivank Garg wrote:

quoted

Replace 'goto skip' with actual logic for better code readability.

No functional change.

Signed-off-by: Shivank Garg <redacted>
---
mm/khugepaged.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 6c8c35d3e0c9..107146f012b1 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c

@@ -2442,14 +2442,15 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,

			break;
		}
		if (!thp_vma_allowable_order(vma, vma->vm_flags, TVA_KHUGEPAGED, PMD_ORDER)) {
-skip:
			progress++;
			continue;
		}
		hstart = round_up(vma->vm_start, HPAGE_PMD_SIZE);
		hend = round_down(vma->vm_end, HPAGE_PMD_SIZE);
-		if (khugepaged_scan.address > hend)
-			goto skip;
+		if (khugepaged_scan.address > hend) {
+			progress++;
+			continue;
+		}

Hi, Shivank

The change here looks good, while I come up with an question.

The @progress here seems record two things:

  * number of pages scaned
  * number of vma skipped

Three things: number of mm. It's incremented 1 for whole khugepaged_scan_mm_slot().

Agree.

quoted

quoted

While in very rare case, we may miss to count the second case.

For example, we have following vmas in a process:

     vma1             vma2
    +----------------+------------+
    |2M              |1M          |
    +----------------+------------+

Let's assume vma1 is exactly HPAGE_PMD_SIZE and also HPAGE_PMD_SIZE aligned.
But vma2 is only half of HPAGE_PMD_SIZE.

When scan finish vma1 and start on vma2, we would have hstart = hend =
address. So we continue here but would not do real scan, since address == hend.

I am thinking whether this could handle it:

		if (khugepaged_scan.address > hend || hend <= hstart) {
			progress++;
			continue;
		}

Do you thinks I am correct on this?

I think you're correct.
IIUC, @progress acts as rate limiter here.

It is increasing +1 for whole, and then increases by +1 per VMA (if skipped),
or by +HPAGE_PMD_NR (if actually scanned).

So, progress ensuring the hugepaged_do_scan run only until (progress >= pages)
at which point it yields and sleeps (wait_event_freezable).

Without your suggested fix, if a process contains a large number of small VMAs (where
round_up hstart >= round_down(hend), it will unfairly consume more CPU cycles before
yielding compared to a process with fewer or aligned VMAs.

You are right. While I am not sure it exists in reality, but in theory it
could be.

quoted

I think your suggestion is ensuring fairness by charging 'progress' count correctly.

Thanks for your confirmation. Would you mind add a cleanup in next version, or
you prefer me to send it :-)

Sure, I'll add this fix patch in the next version.

Thanks,
Shivank