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(p200300d82f25bd000949b5a9e02af265.dip0.t-ipconnect.de. [2003:d8:2f25:bd00:949:b5a9:e02a:f265]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a568a73966sm10525942f8f.34.2025.06.16.00.59.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 16 Jun 2025 00:59:11 -0700 (PDT) Message-ID: Date: Mon, 16 Jun 2025 09:59:09 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/2] mm: Optimize the ARCH_NEEDS_WEAK_PER_CPU logic for s390/alpha architectures To: Hao Ge , Andrew Morton , 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 References: <57e110be6d8387e403b4ef1f3b10714c36afbb51.1750040317.git.gehao@kylinos.cn> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <57e110be6d8387e403b4ef1f3b10714c36afbb51.1750040317.git.gehao@kylinos.cn> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 16.06.25 04:29, Hao Ge wrote: > From: Hao Ge subject is misleading: we are not optimizing anything in this patch, do we? It should probably be called "mm/percpu: rename ARCH_NEEDS_WEAK_PER_CPU to MODULE_NEED_WEAK_PER_CPU" or sth. like that. > > 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 "... 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. > > Therefore,we need to implement isolation for this purpose. In general, throw in a space after "." and "," to make this easier to parse. > > 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. > > Therefore, this patch does the following things: "this patch" should be avoided. "Therefore, let's ..." > Add the ARCH_NEEDS_WEAK_PER_CPU option to the mm Kconfig file > and enable it for the s390 and alpha architectures. > And replace all instances of ARCH_NEEDS_WEAK_PER_CPU > in the kernel code with MODULE_NEEDS_WEAK_PER_CPU. Most of the description here should likely go to patch #2. See below. > > Suggested-by: Suren Baghdasaryan > Signed-off-by: Hao Ge > --- > 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 ++-- > mm/Kconfig | 4 ++++ > 7 files changed, 13 insertions(+), 7 deletions(-) > > diff --git a/arch/alpha/Kconfig b/arch/alpha/Kconfig > index 109a4cddcd13..ce9bc842e384 100644 > --- a/arch/alpha/Kconfig > +++ b/arch/alpha/Kconfig > @@ -7,6 +7,7 @@ config ALPHA > select ARCH_HAS_DMA_OPS if PCI > select ARCH_MIGHT_HAVE_PC_PARPORT > select ARCH_MIGHT_HAVE_PC_SERIO > + select ARCH_NEEDS_WEAK_PER_CPU > select ARCH_NO_PREEMPT > select ARCH_NO_SG_CHAIN > select ARCH_USE_CMPXCHG_LOCKREF > diff --git a/arch/alpha/include/asm/percpu.h b/arch/alpha/include/asm/percpu.h > index 6923249f2d49..b164d3720e9e 100644 > --- a/arch/alpha/include/asm/percpu.h > +++ b/arch/alpha/include/asm/percpu.h > @@ -11,7 +11,7 @@ > * Always use weak definitions for percpu variables in modules. > */ > #if defined(MODULE) && defined(CONFIG_SMP) > -#define ARCH_NEEDS_WEAK_PER_CPU > +#define MODULE_NEEDS_WEAK_PER_CPU > #endif > > #include > diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig > index 0c16dc443e2f..716031d22346 100644 > --- a/arch/s390/Kconfig > +++ b/arch/s390/Kconfig > @@ -132,6 +132,7 @@ config S390 > select ARCH_INLINE_WRITE_UNLOCK_IRQ > select ARCH_INLINE_WRITE_UNLOCK_IRQRESTORE > select ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE > + select ARCH_NEEDS_WEAK_PER_CPU > select ARCH_STACKWALK > select ARCH_SUPPORTS_ATOMIC_RMW > select ARCH_SUPPORTS_DEBUG_PAGEALLOC > diff --git a/arch/s390/include/asm/percpu.h b/arch/s390/include/asm/percpu.h > index 84f6b8357b45..0afc7ce9c26f 100644 > --- a/arch/s390/include/asm/percpu.h > +++ b/arch/s390/include/asm/percpu.h > @@ -18,7 +18,7 @@ > * generate external references. > */ > #if defined(MODULE) > -#define ARCH_NEEDS_WEAK_PER_CPU > +#define MODULE_NEEDS_WEAK_PER_CPU > #endif > > /* > diff --git a/include/linux/alloc_tag.h b/include/linux/alloc_tag.h > index 8f7931eb7d16..f349cca0ebed 100644 > --- a/include/linux/alloc_tag.h > +++ b/include/linux/alloc_tag.h > @@ -88,7 +88,7 @@ static inline struct alloc_tag *ct_to_alloc_tag(struct codetag *ct) > return container_of(ct, struct alloc_tag, ct); > } > > -#ifdef ARCH_NEEDS_WEAK_PER_CPU > +#ifdef MODULE_NEEDS_WEAK_PER_CPU > /* > * When percpu variables are required to be defined as weak, static percpu > * variables can't be used inside a function (see comments for DECLARE_PER_CPU_SECTION). > @@ -102,7 +102,7 @@ DECLARE_PER_CPU(struct alloc_tag_counters, _shared_alloc_tag); > .ct = CODE_TAG_INIT, \ > .counters = &_shared_alloc_tag }; > > -#else /* ARCH_NEEDS_WEAK_PER_CPU */ > +#else /* MODULE_NEEDS_WEAK_PER_CPU */ > > #ifdef MODULE > > @@ -123,7 +123,7 @@ DECLARE_PER_CPU(struct alloc_tag_counters, _shared_alloc_tag); > > #endif /* MODULE */ > > -#endif /* ARCH_NEEDS_WEAK_PER_CPU */ > +#endif /* MODULE_NEEDS_WEAK_PER_CPU */ > > DECLARE_STATIC_KEY_MAYBE(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT, > mem_alloc_profiling_key); > diff --git a/include/linux/percpu-defs.h b/include/linux/percpu-defs.h > index 0aeb0e276a3e..b4ecfc3a7b2b 100644 > --- a/include/linux/percpu-defs.h > +++ b/include/linux/percpu-defs.h > @@ -64,13 +64,13 @@ > * 2. Static percpu variables cannot be defined inside a function. > * > * Archs which need weak percpu definitions should define > - * ARCH_NEEDS_WEAK_PER_CPU in asm/percpu.h when necessary. > + * MODULE_NEEDS_WEAK_PER_CPU in asm/percpu.h when necessary. > * > * To ensure that the generic code observes the above two > * restrictions, if CONFIG_DEBUG_FORCE_WEAK_PER_CPU is set weak > * definition is used for all cases. > */ > -#if defined(ARCH_NEEDS_WEAK_PER_CPU) || defined(CONFIG_DEBUG_FORCE_WEAK_PER_CPU) > +#if defined(MODULE_NEEDS_WEAK_PER_CPU) || defined(CONFIG_DEBUG_FORCE_WEAK_PER_CPU) > /* > * __pcpu_scope_* dummy variable is used to enforce scope. It > * receives the static modifier when it's used in front of > diff --git a/mm/Kconfig b/mm/Kconfig > index e113f713b493..2f55cc95cfcb 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -929,6 +929,10 @@ config ARCH_SUPPORTS_PUD_PFNMAP > def_bool y > depends on ARCH_SUPPORTS_HUGE_PFNMAP && HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD > > +# s390 and alpha should be enabled,see comments for DECLARE_PER_CPU_SECTION > +config ARCH_NEEDS_WEAK_PER_CPU > + bool I agree with Willy that this commit is not ideal -- in particular the "s390 and alpha should be enabled" can get stale easily. If you want to add a comment, rather give guidance why any architecture would want to set this, like: /* Architectures that XXX should set this. */ XXX to be defined. But the bigger problem with this patch is that XXX cannot even be properly defined, because this patch does not make use of CONFIG_ARCH_NEEDS_WEAK_PER_CPU at all. ... that is done in the second patch. So what you could do is move the actual introduction of CONFIG_ARCH_NEEDS_WEAK_PER_CPU to patch #2, where it is actually used, and limit this patch to the rename. Similarly, teak the patch description to reflect only that. -- Cheers, David / dhildenb