linux-kernel - Re: [PATCH v3 0/4] mm: introduce snapshot

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Message-ID: <aHbcBJV04fZoV6wF@hyeyoo>
Date: Wed, 16 Jul 2025 07:53:56 +0900
From: Harry Yoo <harry.yoo@...cle.com>
To: Luiz Capitulino <luizcap@...hat.com>
Cc: david@...hat.com, willy@...radead.org, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org, shivankg@....com,
        sj@...nel.org
Subject: Re: [PATCH v3 0/4] mm: introduce snapshot_page()

On Mon, Jul 14, 2025 at 09:16:50AM -0400, Luiz Capitulino wrote:
> Hi,
> 
> The series introduction will follow the changelog. This is against bc9ff192a6c9 .
> 
> Changelog
> =========
> 
> v2 -> v3
>   - Small snapshot_page() refactor to simplify and fix stack-out-of-bugs bug
>     reported by Harry Yoo
>   - Use clear_compound_head() in snapshot_page() (Shivank)
>   - Read head pointer from ps->page_snapshot() for tail page case (Shivank)
>   - Improve comments and macro name in snapshot_page() (David)
> 
> v1 -> v2
>   - Include is_huge_zero_pfn() patch and use it (David)
>   - Move free page detection to snapshot_page() (David)
>   - Changelog improvements (Shivank)
>   - Added Acked-bys
> 
> RFC -> v1
>   - Include <linux/page_idle.h> to avoid build error on sh arch
> 
> Introduction
> ============
> 
> This series introduces snapshot_page(), a helper function that can be used
> to create a snapshot of a struct page and its associated struct folio.
> 
> This function is intended to help callers with a consistent view of a
> a folio while reducing the chance of encountering partially updated or
> inconsistent state, such as during folio splitting which could lead to
> crashes and BUG_ON()s being triggered.
> 
> David Hildenbrand (1):
>   mm/memory: introduce is_huge_zero_pfn() and use it in
>     vm_normal_page_pmd()
> 
> Luiz Capitulino (3):
>   mm/util: introduce snapshot_page()
>   proc: kpagecount: use snapshot_page()
>   fs: stable_page_flags(): use snapshot_page()
> 
>  fs/proc/page.c          | 50 +++++++++++++++-----------
>  include/linux/huge_mm.h | 12 ++++++-
>  include/linux/mm.h      | 19 ++++++++++
>  mm/debug.c              | 42 +++-------------------
>  mm/memory.c             |  2 +-
>  mm/util.c               | 79 +++++++++++++++++++++++++++++++++++++++++
>  6 files changed, 144 insertions(+), 60 deletions(-)
> 
> --

Haha, I was waiting for this!

The previously reported KASAN splats have completely disappeared on my
testbed.

Please feel free to add,
Tested-by: Harry Yoo <harry.yoo@...cle.com>

-- 
Cheers,
Harry / Hyeonggon