From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-179.mta0.migadu.com (out-179.mta0.migadu.com [91.218.175.179]) (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 E96F817BB6 for ; Wed, 11 Jun 2025 05:27:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.179 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749619674; cv=none; b=n8e3QLus/BufJfTFTq3RoXsp3mD36sGnKIcI3Kuz4WsKcO03wrzrBMBXApc0lMPrvbz1EJfSzDU4fNNUjKY2nGL3Kbz94L1vJmhArCgCaeMrpqWjK9zId0ep8IwTX+5Fj00gIkQYDk/p8JzbxVoy5Y8e9uckw76CsOi7fCL13Ts= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749619674; c=relaxed/simple; bh=VblKf4eUyeI8N6clHN0PxlRzOPLMBcHrTI/YiemJEfM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=p6tVsHuQeP6v2hnmZtuFseLSejgOF25PxWJYRnDU2AHqRFVh6nOSPgNKy48nckmWku7tTYeDCYF4uD8yAo9ItELOOOF0RpBtf9iXfZglaOXDLEy6mDTCvWdzRmpeXZzBnfHaJWVvkqy/CfcOgwZaSGg04TUPJ436sj4vLsoDj9E= 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=a9YMknsx; arc=none smtp.client-ip=91.218.175.179 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="a9YMknsx" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1749619668; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=o/2aaI9Jc+UnnUYnd+8Q2hPmP+rI4bqFnbU4LUmieaM=; b=a9YMknsxGDwTreHyjLWatAFWBw75aBIZM3CGgiYmylO5UHC/vTMRg2bcuNSh0JqBFBFaVA jVEgQE7Oea84sxvFdlirND2HsaaMOufVAeO3p1bx8RAmepeeuy96omvzhwhzxM94YL6Sf0 lndbskN5nteIuGXCNl9qG9CoFexvg3M= Date: Wed, 11 Jun 2025 13:26:52 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH] mm/alloc_tag: add the ARCH_NEEDS_WEAK_PER_CPU macro when statically defining the percpu variable alloc_tag_counters. To: Suren Baghdasaryan Cc: Andrew Morton , Kent Overstreet , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Hao Ge References: <20250529073537.563107-1-hao.ge@linux.dev> <177e1f6b-50f0-4c0a-bb0b-514283e009a2@linux.dev> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Hao Ge In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 2025/6/10 00:39, Suren Baghdasaryan wrote: > On Sun, Jun 8, 2025 at 11:08 PM Hao Ge wrote: >> >> On 2025/5/29 15:35, Hao Ge wrote: >>> 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,there's no need to statically >>> define the percpu variable alloc_tag_counters. >>> >>> Therefore,add therelevant macro guards at the appropriate location. >>> >>> Fixes: 22d407b164ff ("lib: add allocation tagging support for memory allocation profiling") >>> Signed-off-by: Hao Ge >>> --- >>> lib/alloc_tag.c | 2 ++ >>> 1 file changed, 2 insertions(+) >>> >>> diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c >>> index c7f602fa7b23..d1dab80b70ad 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 ARCH_NEEDS_WEAK_PER_CPU >>> DEFINE_PER_CPU(struct alloc_tag_counters, _shared_alloc_tag); >>> EXPORT_SYMBOL(_shared_alloc_tag); >>> +#endif /* ARCH_NEEDS_WEAK_PER_CPU */ >>> >>> DEFINE_STATIC_KEY_MAYBE(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT, >>> mem_alloc_profiling_key); >> Hi Suren >> >> >> I'm sorry to bother you. As mentioned in my commit message, >> >> in fact, on the ARM64 architecture, the _shared_alloc_tag percpu >> variable is not needed. >> >> In my understanding, it will create a copy for each CPU. >> >> The alloc_tag_counters variable will occupy 16 bytes, >> >> and as the number of CPUs increases, more and more memory will be wasted >> in this segment. >> >> I realized that this modification was a mistake. It resulted in a build >> error, and the link is as follows: >> >> https://lore.kernel.org/all/202506080448.KWN8arrX-lkp@intel.com/ >> >> After I studied the comments of DECLARE_PER_CPU_SECTION, I roughly >> understood why this is the case. >> >> But so far, I haven't come up with a good way to solve this problem. Do >> you have any suggestions? > Hi Hao, > The problem here is that ARCH_NEEDS_WEAK_PER_CPU is not a Kconfig > option, it gets defined only on 2 architectures and only when building > modules here https://elixir.bootlin.com/linux/v6.15.1/source/arch/alpha/include/asm/percpu.h#L14 > and here https://elixir.bootlin.com/linux/v6.15.1/source/arch/s390/include/asm/percpu.h#L21. > A nicer way to deal with that is to make if a Kconfig option which is > enabled only for alpha and s390 and then do something like this: > > #if defined(MODULE) && defined(ARCH_NEEDS_WEAK_PER_CPU) > #define MODULE_NEEDS_WEAK_PER_CPU > #endif > > and change all the usages of ARCH_NEEDS_WEAK_PER_CPU with > MODULE_NEEDS_WEAK_PER_CPU. > Did I explain the idea clearly? > Thanks, > Suren. > Hi Suren Thanks for your guidance. I understand this train of thought. I've been thinking about a problem: I only added the ARCH_NEEDS_WEAK_PER_CPU macro to isolate the definition of _shared_alloc_tag. Since s390 defines this macro, why did this build error occur? Could you please help explain it again? Thanks Best Regards Hao >> >> Thanks >> >> Best Regards >> >> Hao >> >> >> >>