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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1749716865; 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=6LY4vo/bZ3YMDxVE6i6Ie0OrWW95nPMauCx+hjveabo=; b=bEhb0s39/6AQKKVdCFbOMmoI15dEpoQaV8yY83TzAs7evlOAtNSZ0+pITLk40TnFfE6ohR fsEV0pa90UGBoDbSZM68jdF1sDyw+t+/u81ktgRZGwp2TkjNMMtM3IEp+aKd/elHEeQPZV Lqbtq7ExfRq0FIb0TeHJWP0Kn7RYMYk= 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 0/5] mm: Restrict the static definition of the per-CPU variable _shared_alloc_tag to s390 and alpha architectures only Date: Thu, 12 Jun 2025 16:27:25 +0800 Message-Id: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 9FDA32000E X-Stat-Signature: zh4tt3k36uparww69ggw1xrimi6hihth X-Rspam-User: X-HE-Tag: 1749716867-383790 X-HE-Meta: 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 qF+r+MIO Tv4SNBccQkwh7do9dsyhIka5vLNnarNZyGysyAXWJetNBf2zUN1/nXLA++Qd72Oly62IyIgDRMwSIUqLV0G1u1BDHerq+bHIBPjc1oxMPj/ileg/PM/Ex/g9EmSUmHsv9T4HHy7eop84QjJV152cDZdEN+gmCmeHq2r6HrVOETS6sr+Ru6bxsnyjzEcRInrGkOFggme465zGUtmKClgyWnjRbcB66akNICm++padQzz6ao6MikcQFKSIKVA== 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,gated by#ifdef CONFIG_ARCH_NEEDS_WEAK_PER_CPU. Then,when defining the percpu variable _shared_alloc_tag,wrap it with the CONFIG_ARCH_NEEDS_WEAK_PER_CPU condition. The following version could be regarded as Version 1: 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 Hao Ge (5): mm/Kconfig: add ARCH_NEEDS_WEAK_PER_CPU option alpha: Modify the definition logic of WEAK_PER_CPU s390: Modify the definition logic of WEAK_PER_CPU mm: use MODULE_NEEDS_WEAK_PER_CPU instead of ARCH_NEEDS_WEAK_PER_CPU 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 | 4 ++-- arch/s390/Kconfig | 1 + arch/s390/include/asm/percpu.h | 4 ++-- include/linux/alloc_tag.h | 6 +++--- include/linux/percpu-defs.h | 4 ++-- lib/alloc_tag.c | 2 ++ mm/Kconfig | 4 ++++ 8 files changed, 17 insertions(+), 9 deletions(-) -- 2.25.1