linux-kernel - Re: [RFC PATCH 2/3] mm/mincore: Use can_pte_batch_count() in mincore_pte_range() for pte batch mincore_pte

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Message-ID: <5fb39e3f-a2d2-496b-9a04-0aa9d33c3189@lucifer.local>
Date: Mon, 27 Oct 2025 19:34:28 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Zhang Qilong <zhangqilong3@...wei.com>
Cc: akpm@...ux-foundation.org, david@...hat.com, Liam.Howlett@...cle.com,
        vbabka@...e.cz, rppt@...nel.org, surenb@...gle.com, mhocko@...e.com,
        jannh@...gle.com, pfalcato@...e.de, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, wangkefeng.wang@...wei.com,
        sunnanyong@...wei.com
Subject: Re: [RFC PATCH 2/3] mm/mincore: Use can_pte_batch_count() in
 mincore_pte_range() for pte batch mincore_pte_range()

On Mon, Oct 27, 2025 at 10:03:14PM +0800, Zhang Qilong wrote:
> In current mincore_pte_range(), if pte_batch_hint() return one
> pte, it's not efficient, just call new added can_pte_batch_count().
>
> In ARM64 qemu, with 8 CPUs, 32G memory, a simple test demo like:
> 1. mmap 1G anon memory
> 2. write 1G data by 4k step
> 3. mincore the mmaped 1G memory
> 4. get the time consumed by mincore
>
> Tested the following cases:
>  - 4k, disabled all hugepage setting.
>  - 64k mTHP, only enable 64k hugepage setting.
>
> Before
>
> Case status | Consumed time (us)  |
> ----------------------------------|
> 4k          | 7356                |
> 64k mTHP    | 3670                |
>
> Pathed:
>
> Case status | Consumed time (us)  |
> ----------------------------------|
> 4k          | 4419                |
> 64k mTHP    | 3061                |
>
> The result is evident and demonstrate a significant improvement in
> the pte batch. While verification within a single environment may
> have inherent randomness. there is a high probability of achieving
> positive effects.

Recent batch PTE series seriously regressed non-arm, so I'm afraid we can't
accept any series that doesn't show statistics for _other platforms_.

Please make sure you at least test x86-64.

This code is very sensitive and we're not going to accept a patch like this
without _being sure_ it's ok.

>
> Signed-off-by: Zhang Qilong <zhangqilong3@...wei.com>
> ---
>  mm/mincore.c | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
>
> diff --git a/mm/mincore.c b/mm/mincore.c
> index 8ec4719370e1..2cc5d276d1cd 100644
> --- a/mm/mincore.c
> +++ b/mm/mincore.c
> @@ -178,18 +178,14 @@ static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
>  		/* We need to do cache lookup too for pte markers */
>  		if (pte_none_mostly(pte))
>  			__mincore_unmapped_range(addr, addr + PAGE_SIZE,
>  						 vma, vec);
>  		else if (pte_present(pte)) {
> -			unsigned int batch = pte_batch_hint(ptep, pte);
> -
> -			if (batch > 1) {
> -				unsigned int max_nr = (end - addr) >> PAGE_SHIFT;
> -
> -				step = min_t(unsigned int, batch, max_nr);
> -			}
> +			unsigned int max_nr = (end - addr) >> PAGE_SHIFT;
>
> +			step = can_pte_batch_count(vma, ptep, &pte,
> +						   max_nr, 0);
>  			for (i = 0; i < step; i++)
>  				vec[i] = 1;
>  		} else { /* pte is a swap entry */
>  			*vec = mincore_swap(pte_to_swp_entry(pte), false);
>  		}
> --
> 2.43.0
>