linux-kernel - [PATCH v2 1/1] mm: Correct misleading comment on mmap_lock field in mm

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Message-Id: <20250806145906.24647-1-adrianhuang0701@gmail.com>
Date: Wed,  6 Aug 2025 22:59:06 +0800
From: "Adrian Huang (Lenovo)" <adrianhuang0701@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: David Hildenbrand <david@...hat.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Liam.Howlett@...cle.com,
	Vlastimil Babka <vbabka@...e.cz>,
	Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>,
	Feng Tang <feng.79.tang@...il.com>,
	ahuang12@...ovo.com,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Adrian Huang <adrianhuang0701@...il.com>
Subject: [PATCH v2 1/1] mm: Correct misleading comment on mmap_lock field in mm_struct

The comment previously described the offset of mmap_lock as 0x120 (hex),
which is misleading. The correct offset is 56 bytes (decimal) from the
last cache line boundary. Using '0x120' could confuse readers trying to
understand why the count and owner fields reside in separate cachelines.

This change also removes an unnecessary space for improved formatting.

Signed-off-by: Adrian Huang (Lenovo) <adrianhuang0701@...il.com>
---
Changes in v2: Per Lorenzo's suggestion, use "56 bytes" instead of 120.

 include/linux/mm_types.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 1ec273b06691..c9c3d0307f8c 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -1026,10 +1026,10 @@ struct mm_struct {
 					     * counters
 					     */
 		/*
-		 * With some kernel config, the current mmap_lock's offset
-		 * inside 'mm_struct' is at 0x120, which is very optimal, as
+		 * Typically the current mmap_lock's offset is 56 bytes from
+		 * the last cacheline boundary, which is very optimal, as
 		 * its two hot fields 'count' and 'owner' sit in 2 different
-		 * cachelines,  and when mmap_lock is highly contended, both
+		 * cachelines, and when mmap_lock is highly contended, both
 		 * of the 2 fields will be accessed frequently, current layout
 		 * will help to reduce cache bouncing.
 		 *
-- 
2.34.1