From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-182.mta1.migadu.com (out-182.mta1.migadu.com [95.215.58.182]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D6F9E2882C7 for ; Mon, 16 Jun 2025 02:30:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750041016; cv=none; b=U2W1PWaqIJyOVfaIwZwbfoJntBwW0VtYVlglcdg5RasCQPBGv2b4VmFXxsc2wYubvIq6KECylrEjjQ4ntxv03itP8B1VEOmDbAPAlTuheL+UO8yeGC9/IM3kl8+8v6y/BFRe+iTLDurxSVEU1PMSOqX9vkzGXEnuQFN8LLcWBhg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750041016; c=relaxed/simple; bh=d99D5Krm7mKYs6va4kUf7uKaI9HolviebMCYWhi1034=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=dTxaFh2YM3hrhgnI9DIy1enk5zZ9Gq1Ofy5/YE0yWfN47Yg3d8p1zBFWBN2GBkr9L6oGsYjH/V2vZxAkVSlb3xjogdX+d550tIv44SdV6cRIkxGfDd/OX5rZJclWzOsX+a9TwBtMviuvT2AW/wsHghIjQ0P/p46NFPz88kELIeI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=DQLERJrq; arc=none smtp.client-ip=95.215.58.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="DQLERJrq" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. 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: Precedence: bulk X-Mailing-List: linux-alpha@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 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