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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1750041008; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=KIW9tIcYwbZjo1QxGJ4orrM2LqJaaYmiNgbtFxQwPmQ=; b=DQLERJrqrvBj5++7xzFmkax2EMVbQ54JQjD5+/QkLzlYUxXiMJXoo9LOzD4hkSs0gixMYm MAOIUR2fQUfrS39XTVuZHhg5c7hsbu+xwNboPoXChPtHGm32av53FS3O0bZQ75nDdol/qY oO2vcvxwFZ+0FwH6uU3jO52/MwioTP8= From: Hao Ge To: Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Suren Baghdasaryan , Mike Rapoport , Richard Henderson , Matt Turner , Dennis Zhou , Tejun Heo , Christoph Lameter , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Kent Overstreet Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-alpha@vger.kernel.org, linux-s390@vger.kernel.org, Hao Ge , Hao Ge Subject: [PATCH v3 0/2] mm: Restrict the static definition of the per-CPU variable _shared_alloc_tag to s390 and alpha architectures only Date: Mon, 16 Jun 2025 10:29:16 +0800 Message-Id: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Queue-Id: 16C0C4000A X-Stat-Signature: w7gfyj6chfktbzbps8yamo3de45xujye X-Rspamd-Server: rspam04 X-HE-Tag: 1750041010-994539 X-HE-Meta: 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 N9y1BYNR TyQ8ej8mS/1jV0tmsGYSzq/K3+iSfPPQLrGkZTx2RnZ2GVBEzffm0Z0FVG3PoGqtVP/eyJyGHy5Za4Tshhj08f6NsAz4k85HmQDUX+hdvyLmJY2VktOKdDFiN2hgtuO6rknMZUb3FaObxfcWl7LNHhqhjiiDVEuo2cdY9rpfi7imPS9pgrftFfCkzL+Rz5hUgGVeivIOO5S2EBaUNxM/3GVlS64ca0pD3Z2lL4V3dWdrP0FCakI5hKJ5RVQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Hao Ge Recently discovered this entry while checking kallsyms on ARM64: ffff800083e509c0 D _shared_alloc_tag If 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. Therefore,we need to implement isolation for this purpose. However,currently ARCH_NEEDS_WEAK_PER_CPU is a #define and is enclosed within the #if defined(MODULE) conditional block. When building the core kernel code for s390 or alpha architectures, ARCH_NEEDS_WEAK_PER_CPU remains undefined (as it is gated by #if defined(MODULE)). However,when building modules for these architectures,the macro is explicitly defined. Therefore,we need to make ARCH_NEEDS_WEAK_PER_CPU a Kconfig option. And replace all instances of ARCH_NEEDS_WEAK_PER_CPU in the kernel code with MODULE_NEEDS_WEAK_PER_CPU,MODULE_NEEDS_WEAK_PER_CPU might be a more accurate description,because it was only needed for modules. Then,when defining the percpu variable _shared_alloc_tag,wrap it with the CONFIG_ARCH_NEEDS_WEAK_PER_CPU condition. The following version can be regarded as the most original version: https://lore.kernel.org/all/20250529073537.563107-1-hao.ge@linux.dev/ But unfortunately,it caused build errors on s390. Based on Suren's guidance and suggestions, I've refined it into this patch series. Many thanks to Suren for his patient instruction. Verify: 1. On Arm64: nm vmlinux | grep "_shared_alloc_tag",no output is returned. 2. On S390: Compile tested. nm vmlinux | grep "_shared_alloc_tag" 00000000015605b4 r __crc__shared_alloc_tag 0000000001585fef r __kstrtab__shared_alloc_tag 0000000001586897 r __kstrtabns__shared_alloc_tag 00000000014f6548 r __ksymtab__shared_alloc_tag 0000000001a8fa28 D _shared_alloc_tag nm net/ceph/libceph.ko | grep "_shared" U _shared_alloc_tag 3. On alpha Compile tested. nm vmlinux | grep "_shared_alloc_tag" fffffc0000b080fa r __kstrtab__shared_alloc_tag fffffc0000b07ee7 r __kstrtabns__shared_alloc_tag fffffc0000adee98 r __ksymtab__shared_alloc_tag fffffc0000b83d38 D _shared_alloc_tag nm crypto/cryptomgr.ko | grep "_share" U _shared_alloc_tag v3: Suren pointed out that patches 1-2 can be merged into a single patch in version 2. And the commit message for patch 3 can be made more concise.Make corresponding modifications based on the pointed-out issues and update the corresponding commit message. v2: Heiko pointed out that when defining MODULE_NEEDS_WEAK_PER_CPU, the CONFIG_ARCH_NEEDS_WEAK_PER_CPU condition in the v1 version should be removed,as it is always true for s390 and alpha architectures.And He also pointed out that patches 2-4 need to be merged into one patch. Modify the code according to the suggestions and update the corresponding commit message. Hao Ge (2): mm: Optimize the ARCH_NEEDS_WEAK_PER_CPU logic for s390/alpha architectures mm/alloc_tag: add the CONFIG_ARCH_NEEDS_WEAK_PER_CPU macro when statically defining the percpu variable _shared_alloc_tag arch/alpha/Kconfig | 1 + arch/alpha/include/asm/percpu.h | 2 +- arch/s390/Kconfig | 1 + arch/s390/include/asm/percpu.h | 2 +- include/linux/alloc_tag.h | 6 +++--- include/linux/percpu-defs.h | 4 ++-- lib/alloc_tag.c | 2 ++ mm/Kconfig | 4 ++++ 8 files changed, 15 insertions(+), 7 deletions(-) -- 2.25.1