linux-kernel - Re: [RFC PATCH 01/11] mm: khugepaged: add khugepaged_max_ptes_none check in collapse

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Message-ID: <9e816c30-8ce9-46dd-99c0-e747df445be9@arm.com>
Date: Wed, 20 Aug 2025 15:43:19 +0530
From: Dev Jain <dev.jain@....com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>, akpm@...ux-foundation.org,
 hughd@...gle.com, david@...hat.com, lorenzo.stoakes@...cle.com
Cc: ziy@...dia.com, Liam.Howlett@...cle.com, npache@...hat.com,
 ryan.roberts@....com, baohua@...nel.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 01/11] mm: khugepaged: add khugepaged_max_ptes_none
 check in collapse_file()


On 20/08/25 2:37 pm, Baolin Wang wrote:
> Similar to the anonymous folios collapse, we should also check the 'khugepaged_max_ptes_none'
> when trying to collapse shmem/file folios.
>
> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> ---
>   mm/khugepaged.c | 7 +++++++
>   1 file changed, 7 insertions(+)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 5a3386043f39..5d4493b77f3c 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -2125,6 +2125,13 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
>   					}
>   				}
>   				nr_none++;
> +
> +				if (cc->is_khugepaged && nr_none > khugepaged_max_ptes_none) {
> +					result = SCAN_EXCEED_NONE_PTE;
> +					count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
> +					goto xa_locked;
> +				}
> +
>   				index++;
>   				continue;
>   			}

Isn't this already being checked in collapse_scan_file(), in the block
if (cc->is_khugepaged && present < HPAGE_PMD_NR - khugepaged_max_ptes_none)?