linux-kernel - [PATCH 3/3] page_counter: reduce struct page

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Message-ID: <20250228075808.207484-4-shakeel.butt@linux.dev>
Date: Thu, 27 Feb 2025 23:58:08 -0800
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Muchun Song <muchun.song@...ux.dev>,
	linux-mm@...ck.org,
	cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Meta kernel team <kernel-team@...a.com>
Subject: [PATCH 3/3] page_counter: reduce struct page_counter size

The struct page_counter has explicit padding for better cache alignment.
The commit c6f53ed8f213a ("mm, memcg: cg2 memory{.swap,}.peak write
handlers") added a field to the struct page_counter and accidently
increased its size. Let's move the failcnt field which is v1-only field
to the same cacheline of usage to reduce the size of struct
page_counter.

Signed-off-by: Shakeel Butt <shakeel.butt@...ux.dev>
---
 include/linux/page_counter.h | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/linux/page_counter.h b/include/linux/page_counter.h
index e4bd8fd427be..d649b6bbbc87 100644
--- a/include/linux/page_counter.h
+++ b/include/linux/page_counter.h
@@ -9,10 +9,12 @@
 
 struct page_counter {
 	/*
-	 * Make sure 'usage' does not share cacheline with any other field. The
-	 * memcg->memory.usage is a hot member of struct mem_cgroup.
+	 * Make sure 'usage' does not share cacheline with any other field in
+	 * v2. The memcg->memory.usage is a hot member of struct mem_cgroup.
 	 */
 	atomic_long_t usage;
+	unsigned long failcnt; /* v1-only field */
+
 	CACHELINE_PADDING(_pad1_);
 
 	/* effective memory.min and memory.min usage tracking */
@@ -28,7 +30,6 @@ struct page_counter {
 	unsigned long watermark;
 	/* Latest cg2 reset watermark */
 	unsigned long local_watermark;
-	unsigned long failcnt; /* v1-only field */
 
 	/* Keep all the read most fields in a separete cacheline. */
 	CACHELINE_PADDING(_pad2_);
-- 
2.43.5