linux-kernel - Re: [PATCH v2 2/3] ksm: perform a range-walk in break

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Message-ID: <cd632ad0-c73e-4e6d-872b-2f4dad285e9d@kernel.org>
Date: Mon, 3 Nov 2025 18:06:26 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: Pedro Demarchi Gomes <pedrodemargomes@...il.com>,
 David Hildenbrand <david@...hat.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: Xu Xin <xu.xin16@....com.cn>, Chengming Zhou <chengming.zhou@...ux.dev>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] ksm: perform a range-walk in break_ksm

On 31.10.25 18:46, Pedro Demarchi Gomes wrote:
> Make break_ksm() receive an address range and change
> break_ksm_pmd_entry() to perform a range-walk and return the address of
> the first ksm page found.
> 
> This change allows break_ksm() to skip unmapped regions instead of
> iterating every page address. When unmerging large sparse VMAs, this
> significantly reduces runtime.
> 
> In a benchmark unmerging a 32 TiB sparse virtual address space where
> only one page was populated, the runtime dropped from 9 minutes to less
> then 5 seconds.
> 
> Suggested-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Pedro Demarchi Gomes <pedrodemargomes@...il.com>
> ---
>   mm/ksm.c | 88 ++++++++++++++++++++++++++++++--------------------------
>   1 file changed, 48 insertions(+), 40 deletions(-)
> 
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 922d2936e206..64d66699133d 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -607,35 +607,55 @@ static inline bool ksm_test_exit(struct mm_struct *mm)
>   	return atomic_read(&mm->mm_users) == 0;
>   }
>   
> -static int break_ksm_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long next,
> +struct break_ksm_arg {
> +	unsigned long addr;
> +};

Leftover? :)

> +
> +static int break_ksm_pmd_entry(pmd_t *pmdp, unsigned long addr, unsigned long end,
>   			struct mm_walk *walk)
>   {
> -	struct folio *folio = NULL;
> +	unsigned long *found_addr = (unsigned long *) walk->private;
> +	struct mm_struct *mm = walk->mm;
> +	pte_t *start_ptep, *ptep;
>   	spinlock_t *ptl;
> -	pte_t *pte;
> -	pte_t ptent;
> -	int ret;
> +	int found = 0;

Best to perform the ret -> found rename already in patch #1.


With both things

Acked-by: David Hildenbrand (Red Hat) <david@...nel.org>

-- 
Cheers

David