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[2003:cb:c71a:5900:d106:4706:528a:7cd5]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-39d893611dcsm4754879f8f.9.2025.04.10.06.18.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 10 Apr 2025 06:18:01 -0700 (PDT) Message-ID: <9deb3725-8991-43d1-8c3d-56523fabff28@redhat.com> Date: Thu, 10 Apr 2025 15:18:00 +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] drivers/base/memory: Avoid overhead from for_each_present_section_nr() To: Gavin Shan , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, adityag@linux.ibm.com, donettom@linux.ibm.com, osalvador@suse.de, gregkh@linuxfoundation.org, rafael@kernel.org, dakr@kernel.org, akpm@linux-foundation.org, shan.gavin@gmail.com References: <20250410125110.1232329-1-gshan@redhat.com> 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: <20250410125110.1232329-1-gshan@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 10.04.25 14:51, Gavin Shan wrote: > for_each_present_section_nr() was introduced to add_boot_memory_block() > by commit 61659efdb35c ("drivers/base/memory: improve add_boot_memory_block()"). > It causes unnecessary overhead when the present sections are really > sparse. next_present_section_nr() called by the macro to find the next > present section, which is far away from the spanning sections in the > specified block. Too much time consumed by next_present_section_nr() > in this case, which can lead to softlockup as observed by Aditya Gupta > on IBM Power10 machine. > > watchdog: BUG: soft lockup - CPU#248 stuck for 22s! [swapper/248:1] > Modules linked in: > CPU: 248 UID: 0 PID: 1 Comm: swapper/248 Not tainted 6.15.0-rc1-next-20250408 #1 VOLUNTARY > Hardware name: 9105-22A POWER10 (raw) 0x800200 opal:v7.1-107-gfda75d121942 PowerNV > NIP: c00000000209218c LR: c000000002092204 CTR: 0000000000000000 > REGS: c00040000418fa30 TRAP: 0900 Not tainted (6.15.0-rc1-next-20250408) > MSR: 9000000002009033 CR: 28000428 XER: 00000000 > CFAR: 0000000000000000 IRQMASK: 0 > GPR00: c000000002092204 c00040000418fcd0 c000000001b08100 0000000000000040 > GPR04: 0000000000013e00 c000c03ffebabb00 0000000000c03fff c000400fff587f80 > GPR08: 0000000000000000 00000000001196f7 0000000000000000 0000000028000428 > GPR12: 0000000000000000 c000000002e80000 c00000000001007c 0000000000000000 > GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 > GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 > GPR24: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 > GPR28: c000000002df7f70 0000000000013dc0 c0000000011dd898 0000000008000000 > NIP [c00000000209218c] memory_dev_init+0x114/0x1e0 > LR [c000000002092204] memory_dev_init+0x18c/0x1e0 > Call Trace: > [c00040000418fcd0] [c000000002092204] memory_dev_init+0x18c/0x1e0 (unreliable) > [c00040000418fd50] [c000000002091348] driver_init+0x78/0xa4 > [c00040000418fd70] [c0000000020063ac] kernel_init_freeable+0x22c/0x370 > [c00040000418fde0] [c0000000000100a8] kernel_init+0x34/0x25c > [c00040000418fe50] [c00000000000cd94] ret_from_kernel_user_thread+0x14/0x1c > > Avoid the overhead by folding for_each_present_section_nr() to the outer > loop. add_boot_memory_block() is dropped after that. > > Fixes: 61659efdb35c ("drivers/base/memory: improve add_boot_memory_block()") > Closes: https://lore.kernel.org/linux-mm/20250409180344.477916-1-adityag@linux.ibm.com > Reported-by: Aditya Gupta > Signed-off-by: Gavin Shan > --- > drivers/base/memory.c | 41 +++++++++++++++++------------------------ > 1 file changed, 17 insertions(+), 24 deletions(-) > > diff --git a/drivers/base/memory.c b/drivers/base/memory.c > index 8f3a41d9bfaa..19469e7f88c2 100644 > --- a/drivers/base/memory.c > +++ b/drivers/base/memory.c > @@ -816,21 +816,6 @@ static int add_memory_block(unsigned long block_id, unsigned long state, > return 0; > } > > -static int __init add_boot_memory_block(unsigned long base_section_nr) > -{ > - unsigned long nr; > - > - for_each_present_section_nr(base_section_nr, nr) { > - if (nr >= (base_section_nr + sections_per_block)) > - break; > - > - return add_memory_block(memory_block_id(base_section_nr), > - MEM_ONLINE, NULL, NULL); > - } > - > - return 0; > -} > - > static int add_hotplug_memory_block(unsigned long block_id, > struct vmem_altmap *altmap, > struct memory_group *group) > @@ -957,7 +942,7 @@ static const struct attribute_group *memory_root_attr_groups[] = { > void __init memory_dev_init(void) > { > int ret; > - unsigned long block_sz, nr; > + unsigned long block_sz, block_id, nr; > > /* Validate the configured memory block size */ > block_sz = memory_block_size_bytes(); > @@ -970,15 +955,23 @@ void __init memory_dev_init(void) > panic("%s() failed to register subsystem: %d\n", __func__, ret); > > /* > - * Create entries for memory sections that were found > - * during boot and have been initialized > + * Create entries for memory sections that were found during boot > + * and have been initialized. Use @block_id to track the last > + * handled block and initialize it to an invalid value (ULONG_MAX) > + * to bypass the block ID matching check for the first present > + * block so that it can be covered. > */ > - for (nr = 0; nr <= __highest_present_section_nr; > - nr += sections_per_block) { > - ret = add_boot_memory_block(nr); > - if (ret) > - panic("%s() failed to add memory block: %d\n", __func__, > - ret); > + block_id = ULONG_MAX; > + for_each_present_section_nr(0, nr) { > + if (block_id != ULONG_MAX && memory_block_id(nr) == block_id) > + continue; > + > + block_id = memory_block_id(nr); > + ret = add_memory_block(block_id, MEM_ONLINE, NULL, NULL); > + if (ret) { > + panic("%s() failed to add memory block: %d\n", > + __func__, ret); > + } > } > } > Staring at the end result and the particularly long comment, are we now really any better than before 61659efdb35c? Revert instead? -- Cheers, David / dhildenb