linux-kernel - [PATCH 5/5] mm/alloc_tag: add the CONFIG_ARCH_NEEDS_WEAK_PER_CPU macro when statically defining the percpu variable _shared_alloc

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Message-Id: <adcd63180c9492361d929019c60ffa942255988a.1749715979.git.gehao@kylinos.cn>
Date: Thu, 12 Jun 2025 16:27:30 +0800
From: Hao Ge <hao.ge@...ux.dev>
To: Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...hat.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Mike Rapoport <rppt@...nel.org>,
	Richard Henderson <richard.henderson@...aro.org>,
	Matt Turner <mattst88@...il.com>,
	Dennis Zhou <dennis@...nel.org>,
	Tejun Heo <tj@...nel.org>,
	Christoph Lameter <cl@...ux.com>,
	Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Sven Schnelle <svens@...ux.ibm.com>,
	Kent Overstreet <kent.overstreet@...ux.dev>
Cc: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	linux-alpha@...r.kernel.org,
	linux-s390@...r.kernel.org,
	Hao Ge <hao.ge@...ux.dev>,
	Hao Ge <gehao@...inos.cn>
Subject: [PATCH 5/5] mm/alloc_tag: add the CONFIG_ARCH_NEEDS_WEAK_PER_CPU macro when statically defining the percpu variable _shared_alloc_tag

From: Hao Ge <gehao@...inos.cn>

Recently discovered this entry while checking kallsyms on ARM64:
ffff800083e509c0 D _shared_alloc_tag

If CONFIG_ARCH_NEEDS_WEAK_PER_CPU is not defined(it is only defined for
s390 and alpha architectures),there's no need to statically define
the percpu variable _shared_alloc_tag. As the number of CPUs
increases,the wasted memory will grow correspondingly.

Enclose the definition of _shared_alloc_tag within the
CONFIG_ARCH_NEEDS_WEAK_PER_CPU condition.

Suggested-by: Suren Baghdasaryan <surenb@...gle.com>
Signed-off-by: Hao Ge <gehao@...inos.cn>
---
 lib/alloc_tag.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
index c7f602fa7b23..14fd66f26e42 100644
--- a/lib/alloc_tag.c
+++ b/lib/alloc_tag.c
@@ -24,8 +24,10 @@ static bool mem_profiling_support;
 
 static struct codetag_type *alloc_tag_cttype;
 
+#ifdef CONFIG_ARCH_NEEDS_WEAK_PER_CPU
 DEFINE_PER_CPU(struct alloc_tag_counters, _shared_alloc_tag);
 EXPORT_SYMBOL(_shared_alloc_tag);
+#endif
 
 DEFINE_STATIC_KEY_MAYBE(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,
 			mem_alloc_profiling_key);
-- 
2.25.1