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[2003:cb:c739:2400:78ac:64bb:a39e:2578]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3675a1046f2sm12181737f8f.112.2024.07.01.23.57.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 01 Jul 2024 23:57:58 -0700 (PDT) Message-ID: Date: Tue, 2 Jul 2024 08:57:57 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/page_alloc: remove prefetchw() on freeing page to buddy system To: Wei Yang , akpm@linux-foundation.org Cc: linux-mm@kvack.org, willy@infradead.org References: <20240702020931.7061-1-richard.weiyang@gmail.com> From: David Hildenbrand 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: <20240702020931.7061-1-richard.weiyang@gmail.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: DA8661A0010 X-Stat-Signature: 4jyyommw9x97yc64bzaydwz6qokodo1k X-Rspam-User: X-HE-Tag: 1719903482-831739 X-HE-Meta: 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 iqFJh2iU 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 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: On 02.07.24 04:09, Wei Yang wrote: > The prefetchw() is introduced from an ancient patch[1]. > > The change log says: > > The basic idea is to free higher order pages instead of going > through every single one. Also, some unnecessary atomic operations > are done away with and replaced with non-atomic equivalents, and > prefetching is done where it helps the most. For a more in-depth > discusion of this patch, please see the linux-ia64 archives (topic > is "free bootmem feedback patch"). > > So there are several changes improve the bootmem freeing, in which the > most basic idea is freeing higher order pages. And as Matthew says, > "Itanium CPUs of this era had no prefetchers." > > I did 10 round bootup tests before and after this change, the data > doesn't prove prefetchw() help speeding up bootmem freeing. The sum of > the 10 round bootmem freeing time after prefetchw() removal even 5.2% > faster than before. I suspect this is noise, though. > > [1]: https://lore.kernel.org/linux-ia64/40F46962.4090604@sgi.com/ > > Signed-off-by: Wei Yang > Suggested-by: Matthew Wilcox > CC: David Hildenbrand > > --- > The patch is based on mm-stable with David's change. > --- > mm/page_alloc.c | 13 ++----------- > 1 file changed, 2 insertions(+), 11 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 116ee33fd1ce..c46aedfc9a12 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1236,16 +1236,11 @@ void __meminit __free_pages_core(struct page *page, unsigned int order, > */ > if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG) && > unlikely(context == MEMINIT_HOTPLUG)) { > - prefetchw(p); > - for (loop = 0; loop < (nr_pages - 1); loop++, p++) { > - prefetchw(p + 1); > + for (loop = 0; loop < nr_pages; loop++, p++) { > VM_WARN_ON_ONCE(PageReserved(p)); > __ClearPageOffline(p); > set_page_count(p, 0); > } Something like: for (;;) { ... if (++loop >= nr_pages) break; p++; } Might generate slightly better code, because we know that we execute the loop body at least once. We use that in set_ptes(), for example. > - VM_WARN_ON_ONCE(PageReserved(p)); > - __ClearPageOffline(p); > - set_page_count(p, 0); > > /* > * Freeing the page with debug_pagealloc enabled will try to > @@ -1255,14 +1250,10 @@ void __meminit __free_pages_core(struct page *page, unsigned int order, > debug_pagealloc_map_pages(page, nr_pages); > adjust_managed_page_count(page, nr_pages); > } else { > - prefetchw(p); > - for (loop = 0; loop < (nr_pages - 1); loop++, p++) { > - prefetchw(p + 1); > + for (loop = 0; loop < nr_pages; loop++, p++) { > __ClearPageReserved(p); > set_page_count(p, 0); > } > - __ClearPageReserved(p); > - set_page_count(p, 0); > > /* memblock adjusts totalram_pages() manually. */ > atomic_long_add(nr_pages, &page_zone(page)->managed_pages); Much better Reviewed-by: David Hildenbrand -- Cheers, David / dhildenb