+ mm-optimize-the-implementation-of-warn_on_once_gfp.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm: optimize the implementation of WARN_ON_ONCE_GFP()
has been added to the -mm mm-new branch.  Its filename is
     mm-optimize-the-implementation-of-warn_on_once_gfp.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-optimize-the-implementation-of-warn_on_once_gfp.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
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: Xie Yuanbin <qq570070308@gmail.com>
Subject: mm: optimize the implementation of WARN_ON_ONCE_GFP()
Date: Mon, 9 Mar 2026 23:38:11 +0800

As shown in the commit message of commit 242b872239f6a7deacbc
("include/linux/once_lite.h: fix judgment in WARN_ONCE with clang"), the
code "unlikely(a && b)" may generate poor assembly code if it is actually
"unlikely(a) && unlikely(b)" or "unlikely(a) && b".

WARN_ON_ONCE_GFP() may be used in the hot path code:
1. The argument cond shoud be unlikely.
2. When "1." is true, !(gfp & __GFP_NOWARN) is unlikely, otherwise, a
   WARN may be triggered, which is a very unlikely case.
3. When "1. && 2." is true, just like the implementation of WARN_ONCE(),
   !__warned can be unlikely.

Reorder __ret_warn_once judgement to first and split out the unlikely() in
WARN_ON_ONCE_GFP() to optimize performance.

Link: https://lkml.kernel.org/r/20260309153811.40958-1-qq570070308@gmail.com
Signed-off-by: Xie Yuanbin <qq570070308@gmail.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Bill Wendling <morbo@google.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Justin Stitt <justinstitt@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/internal.h |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/mm/internal.h~mm-optimize-the-implementation-of-warn_on_once_gfp
+++ a/mm/internal.h
@@ -94,7 +94,8 @@ struct pagetable_move_control {
 	static bool __section(".data..once") __warned;			\
 	int __ret_warn_once = !!(cond);					\
 									\
-	if (unlikely(!(gfp & __GFP_NOWARN) && __ret_warn_once && !__warned)) { \
+	if (unlikely(__ret_warn_once) &&				\
+	    unlikely(!(gfp & __GFP_NOWARN)) && unlikely(!__warned)) {	\
 		__warned = true;					\
 		WARN_ON(1);						\
 	}								\
_

Patches currently in -mm which might be from qq570070308@gmail.com are

mm-optimize-the-implementation-of-warn_on_once_gfp.patch