linux-kernel - Re: [PATCH mm-new v6 2/5] mm: khugepaged: refine scan progress number

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Message-ID: <fd67a91f-3930-4bd8-886b-13f7783f4aec@kernel.org>
Date: Wed, 4 Feb 2026 22:35:48 +0100
From: "David Hildenbrand (arm)" <david@...nel.org>
To: Vernon Yang <vernon2gm@...il.com>, akpm@...ux-foundation.org
Cc: lorenzo.stoakes@...cle.com, ziy@...dia.com, dev.jain@....com,
 baohua@...nel.org, lance.yang@...ux.dev, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, Vernon Yang <yanglincheng@...inos.cn>
Subject: Re: [PATCH mm-new v6 2/5] mm: khugepaged: refine scan progress number

[...]

> +	if (cur_progress) {
> +		if (_pte >= pte + HPAGE_PMD_NR)
> +			*cur_progress = HPAGE_PMD_NR;
> +		else
> +			*cur_progress = _pte - pte + 1;

*cur_progress = max(_pte - pte + 1, HPAGE_PMD_NR);

?

It's still a bit nasty, though.

Can't we just add one at the beginning of the loop and let the compiler
optimize that? ;)

> +	}
>   	pte_unmap_unlock(pte, ptl);
>   	if (result == SCAN_SUCCEED) {
>   		result = collapse_huge_page(mm, start_addr, referenced,
> @@ -2286,8 +2301,9 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
>   	return result;
>   }
>   
> -static enum scan_result hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
> -		struct file *file, pgoff_t start, struct collapse_control *cc)
> +static enum scan_result hpage_collapse_scan_file(struct mm_struct *mm,
> +		unsigned long addr, struct file *file, pgoff_t start,
> +		unsigned int *cur_progress, struct collapse_control *cc)
>   {
>   	struct folio *folio = NULL;
>   	struct address_space *mapping = file->f_mapping;
> @@ -2376,6 +2392,8 @@ static enum scan_result hpage_collapse_scan_file(struct mm_struct *mm, unsigned
>   			cond_resched_rcu();
>   		}
>   	}
> +	if (cur_progress)
> +		*cur_progress = max(xas.xa_index - start, 1UL);
I would really just keep it simple here and do a

*cur_progress = HPAGE_PMD_NR;

This stuff is hard to reason about, so I would just leave the file case 
essentially unchanged.

IIRC, it would not affect the numbers you report in the patch description?

-- 
Cheers,

David