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

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Message-ID: <20251217024818.ngoime34bxeatqij@master>
Date: Wed, 17 Dec 2025 02:48:18 +0000
From: Wei Yang <richard.weiyang@...il.com>
To: Shivank Garg <shivankg@....com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...nel.org>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Zi Yan <ziy@...dia.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	"Liam R . Howlett" <Liam.Howlett@...cle.com>,
	Nico Pache <npache@...hat.com>, Ryan Roberts <ryan.roberts@....com>,
	Dev Jain <dev.jain@....com>, Barry Song <baohua@...nel.org>,
	Lance Yang <lance.yang@...ux.dev>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] mm/khugepaged: remove unnecessary goto 'skip' label

On Tue, Dec 16, 2025 at 11:11:38AM +0000, Shivank Garg wrote:
>Replace 'goto skip' with actual logic for better code readability.
>
>No functional change.
>
>Signed-off-by: Shivank Garg <shivankg@....com>
>---
> 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

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?

> 		if (khugepaged_scan.address < hstart)
> 			khugepaged_scan.address = hstart;
> 		VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
>-- 
>2.43.0
>

-- 
Wei Yang
Help you, Help me