+ pagemap-update-buddy-flag-documentation.patch added to mm-new branch

+ pagemap-update-buddy-flag-documentation.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: pagemap: update BUDDY flag documentation
has been added to the -mm mm-new branch.  Its filename is
     pagemap-update-buddy-flag-documentation.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/pagemap-update-buddy-flag-documentation.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

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------------------------------------------------------
From: Richard Weinberger <richard@nod.at>
Subject: pagemap: update BUDDY flag documentation
Date: Sat, 22 Nov 2025 22:19:20 +0100

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.

Link: https://lkml.kernel.org/r/20251122211920.3410371-1-richard@nod.at
Signed-off-by: Richard Weinberger <richard@nod.at>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 Documentation/admin-guide/mm/pagemap.rst |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/Documentation/admin-guide/mm/pagemap.rst~pagemap-update-buddy-flag-documentation
+++ a/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
_

Patches currently in -mm which might be from richard@nod.at are

pagemap-update-buddy-flag-documentation.patch