linux-kernel - Re: [PATCH v5 3/7] mm: Add batched versions of ptep_modify_prot

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Message-ID: <CAGsJ_4xiUZzQNR57qpebcwKxV1T_S90j-=Z0EQ0s=1u3Q7rG8w@mail.gmail.com>
Date: Mon, 21 Jul 2025 07:59:39 +0800
From: Barry Song <21cnbao@...il.com>
To: Dev Jain <dev.jain@....com>
Cc: akpm@...ux-foundation.org, ryan.roberts@....com, david@...hat.com, 
	willy@...radead.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	catalin.marinas@....com, will@...nel.org, Liam.Howlett@...cle.com, 
	lorenzo.stoakes@...cle.com, vbabka@...e.cz, jannh@...gle.com, 
	anshuman.khandual@....com, peterx@...hat.com, joey.gouly@....com, 
	ioworker0@...il.com, kevin.brodsky@....com, quic_zhenhuah@...cinc.com, 
	christophe.leroy@...roup.eu, yangyicong@...ilicon.com, 
	linux-arm-kernel@...ts.infradead.org, hughd@...gle.com, 
	yang@...amperecomputing.com, ziy@...dia.com
Subject: Re: [PATCH v5 3/7] mm: Add batched versions of ptep_modify_prot_start/commit

On Fri, Jul 18, 2025 at 5:03 PM Dev Jain <dev.jain@....com> wrote:
>
> Batch ptep_modify_prot_start/commit in preparation for optimizing mprotect,
> implementing them as a simple loop over the corresponding single pte
> helpers. Architecture may override these helpers.
>
> Signed-off-by: Dev Jain <dev.jain@....com>

Reviewed-by: Barry Song <baohua@...nel.org>

> ---
>  include/linux/pgtable.h | 84 ++++++++++++++++++++++++++++++++++++++++-
>  mm/mprotect.c           |  4 +-
>  2 files changed, 85 insertions(+), 3 deletions(-)
>

[...]

> +#ifndef modify_prot_start_ptes
> +static inline pte_t modify_prot_start_ptes(struct vm_area_struct *vma,
> +               unsigned long addr, pte_t *ptep, unsigned int nr)
> +{
> +       pte_t pte, tmp_pte;
> +
> +       pte = ptep_modify_prot_start(vma, addr, ptep);
> +       while (--nr) {
> +               ptep++;
> +               addr += PAGE_SIZE;
> +               tmp_pte = ptep_modify_prot_start(vma, addr, ptep);
> +               if (pte_dirty(tmp_pte))
> +                       pte = pte_mkdirty(pte);
> +               if (pte_young(tmp_pte))
> +                       pte = pte_mkyoung(pte);

It might be interesting to explore whether a similar optimization
could apply here as well:
https://lore.kernel.org/linux-mm/20250624152549.2647828-1-xavier.qyxia@gmail.com/
I suspect it would, but it's probably not worth including in this
patch.

> +       }
> +       return pte;
> +}
> +#endif
> +

Thanks
Barry