* Re: [PATCH] pagemap: Update BUDDY flag documentation
2025-11-22 21:19 [PATCH] pagemap: Update BUDDY flag documentation Richard Weinberger
@ 2025-11-23 9:29 ` Mike Rapoport
2025-11-24 10:47 ` David Hildenbrand (Red Hat)
2025-11-24 10:51 ` Lorenzo Stoakes
2 siblings, 0 replies; 4+ messages in thread
From: Mike Rapoport @ 2025-11-23 9:29 UTC (permalink / raw)
To: Richard Weinberger
Cc: linux-mm, linux-doc, linux-kernel, corbet, mhocko, surenb,
vbabka, Liam.Howlett, lorenzo.stoakes, david, akpm,
Vladimir Davydov, Konstantin Khlebnikov, Naoya Horiguchi,
Linus Torvalds
On Sat, Nov 22, 2025 at 10:19:20PM +0100, Richard Weinberger wrote:
> Since v4.6 the BUDDY flag is set for _all_ pages in the block
> and no longer just for the first one.
> This change was introduced by:
> commit 832fc1de01ae ("/proc/kpageflags: return KPF_BUDDY for "tail" buddy pages")
>
> Strictly speaking, this was an ABI change, but as nobody has noticed
> since 2016, let's just update the documentation.
>
> Cc: Vladimir Davydov <vdavydov@virtuozzo.com>>
> Cc: Konstantin Khlebnikov <koct9i@gmail.com>
> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Richard Weinberger <richard@nod.at>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> ---
> Documentation/admin-guide/mm/pagemap.rst | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst
> index e60e9211fd9b2..c57e61b5d8aa8 100644
> --- a/Documentation/admin-guide/mm/pagemap.rst
> +++ b/Documentation/admin-guide/mm/pagemap.rst
> @@ -115,7 +115,8 @@ Short descriptions to the page flags
> A free memory block managed by the buddy system allocator.
> The buddy system organizes free memory in blocks of various orders.
> An order N block has 2^N physically contiguous pages, with the BUDDY flag
> - set for and _only_ for the first page.
> + set for all pages.
> + Before 4.6 only the first page of the block had the flag set.
> 15 - COMPOUND_HEAD
> A compound page with order N consists of 2^N physically contiguous pages.
> A compound page with order 2 takes the form of "HTTT", where H donates its
> --
> 2.51.0
>
>
--
Sincerely yours,
Mike.
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] pagemap: Update BUDDY flag documentation
2025-11-22 21:19 [PATCH] pagemap: Update BUDDY flag documentation Richard Weinberger
2025-11-23 9:29 ` Mike Rapoport
@ 2025-11-24 10:47 ` David Hildenbrand (Red Hat)
2025-11-24 10:51 ` Lorenzo Stoakes
2 siblings, 0 replies; 4+ messages in thread
From: David Hildenbrand (Red Hat) @ 2025-11-24 10:47 UTC (permalink / raw)
To: Richard Weinberger, linux-mm
Cc: linux-doc, linux-kernel, corbet, mhocko, surenb, rppt, vbabka,
Liam.Howlett, lorenzo.stoakes, akpm, Vladimir Davydov,
Konstantin Khlebnikov, Naoya Horiguchi, Linus Torvalds
On 11/22/25 22:19, Richard Weinberger wrote:
> Since v4.6 the BUDDY flag is set for _all_ pages in the block
> and no longer just for the first one.
> This change was introduced by:
> commit 832fc1de01ae ("/proc/kpageflags: return KPF_BUDDY for "tail" buddy pages")
>
> Strictly speaking, this was an ABI change, but as nobody has noticed
> since 2016, let's just update the documentation.
>
> Cc: Vladimir Davydov <vdavydov@virtuozzo.com>>
> Cc: Konstantin Khlebnikov <koct9i@gmail.com>
> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Richard Weinberger <richard@nod.at>
> ---
Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
--
Cheers
David
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] pagemap: Update BUDDY flag documentation
2025-11-22 21:19 [PATCH] pagemap: Update BUDDY flag documentation Richard Weinberger
2025-11-23 9:29 ` Mike Rapoport
2025-11-24 10:47 ` David Hildenbrand (Red Hat)
@ 2025-11-24 10:51 ` Lorenzo Stoakes
2 siblings, 0 replies; 4+ messages in thread
From: Lorenzo Stoakes @ 2025-11-24 10:51 UTC (permalink / raw)
To: Richard Weinberger
Cc: linux-mm, linux-doc, linux-kernel, corbet, mhocko, surenb, rppt,
vbabka, Liam.Howlett, david, akpm, Vladimir Davydov,
Konstantin Khlebnikov, Naoya Horiguchi, Linus Torvalds
On Sat, Nov 22, 2025 at 10:19:20PM +0100, Richard Weinberger wrote:
> Since v4.6 the BUDDY flag is set for _all_ pages in the block
> and no longer just for the first one.
> This change was introduced by:
> commit 832fc1de01ae ("/proc/kpageflags: return KPF_BUDDY for "tail" buddy pages")
>
> Strictly speaking, this was an ABI change, but as nobody has noticed
> since 2016, let's just update the documentation.
>
> Cc: Vladimir Davydov <vdavydov@virtuozzo.com>>
> Cc: Konstantin Khlebnikov <koct9i@gmail.com>
> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Richard Weinberger <richard@nod.at>
Good catch! LGTM, so:
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> ---
> Documentation/admin-guide/mm/pagemap.rst | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst
> index e60e9211fd9b2..c57e61b5d8aa8 100644
> --- a/Documentation/admin-guide/mm/pagemap.rst
> +++ b/Documentation/admin-guide/mm/pagemap.rst
> @@ -115,7 +115,8 @@ Short descriptions to the page flags
> A free memory block managed by the buddy system allocator.
> The buddy system organizes free memory in blocks of various orders.
> An order N block has 2^N physically contiguous pages, with the BUDDY flag
> - set for and _only_ for the first page.
> + set for all pages.
> + Before 4.6 only the first page of the block had the flag set.
> 15 - COMPOUND_HEAD
> A compound page with order N consists of 2^N physically contiguous pages.
> A compound page with order 2 takes the form of "HTTT", where H donates its
> --
> 2.51.0
>
^ permalink raw reply [flat|nested] 4+ messages in thread