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[2003:cb:c736:ca00:b4c3:24bd:c2f5:863c]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-438bd47f0fdsm139928195e9.5.2025.01.27.08.20.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 27 Jan 2025 08:20:27 -0800 (PST) Message-ID: <503c29c8-bcc7-4a6c-ab2e-ebf238a9a1db@redhat.com> Date: Mon, 27 Jan 2025 17:20:25 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: Direct I/O performance problems with 1GB pages From: David Hildenbrand To: Matthew Wilcox Cc: linux-mm@kvack.org, linux-block@vger.kernel.org, Muchun Song , Jane Chu , Andres Freund References: 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: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: vvh6a_JQYSkIZAEu7_4rLsoDlZGNvm7me7Gr9VSGnhs_1737994828 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: rspam02 X-Rspamd-Queue-Id: 6A3A81C0013 X-Stat-Signature: tt5pyj4ieym817xtfe4yptjizw96z1x3 X-Rspam-User: X-HE-Tag: 1737994835-589694 X-HE-Meta: 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 FO1ST19O pslfyFwGQwPw9P4+b+ktDwhIPb8LRDgAYN/U+pRyDBJSdOwNUtGmJgm6xDw0gDy5Cr0fci35WPIaP47Ix0ikSM+VelcaYzKwVQUSpFi+Z6f0G2BDrkpp5NS8/COJAci8mjEnSON7cAB7zIDv5aC4sgTcKfx5nnk19IBkOVsoP+iW0nMBfQWOKHL5cX/BLiDbGFGL+d324cPD1nrbq+IseRV/Yxm1tOf4N8z8TtXtTX9tVtnMjvikbMJYJf23DN6n2f+YuRTLZ9o1ysE/CSjNbAyw9BueBcqpw70BZAOX9ZjMRNmPdDycHtpx1KhTgvGgLSzzXO1ADlVbS01RixvCufR8IMYcos74Ij9K1rn8mGAjADGAa+dEwUPcL5GM+WBfHfWVYGeveQQq8bXI= 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 27.01.25 17:09, David Hildenbrand wrote: >> >>> If the workload doing a lot of single-page try_grab_folio_fast(), could it >>> do so on a larger area (multiple pages at once -> single refcount update)? >> >> Not really. This is memory that's being used as the buffer cache, so >> every thread in your database is hammering on it and pulling in exactly >> the data that it needs for the SQL query that it's processing. > > Ouch. > >> >>> Maybe there is a link to the report you could share, thanks. >> >> Andres shared some gists, but I don't want to send those to a >> mailing list without permission. Here's the kernel part of the >> perf report: >> >> 14.04% postgres [kernel.kallsyms] [k] try_grab_folio_fast >> | >> --14.04%--try_grab_folio_fast >> gup_fast_fallback >> | >> --13.85%--iov_iter_extract_pages >> bio_iov_iter_get_pages >> iomap_dio_bio_iter >> __iomap_dio_rw >> iomap_dio_rw >> xfs_file_dio_read >> xfs_file_read_iter >> __io_read >> io_read >> io_issue_sqe >> io_submit_sqes >> __do_sys_io_uring_enter >> do_syscall_64 BTW, two things that come to mind: (1) We always fallback to GUP-fast, I wonder why. GUP-fast would go via try_grab_folio_fast(). (2) During GUP slow, we must take the PT lock of the PUD table. So the folio refcount/pincount/whatever is actually sync'ed by the ... PT lock here? See assert_spin_locked(pud_lockptr(mm, pudp)); in follow_huge_pud(). Note that that PUD table lock is likely a per-MM lock ... and yes, it indeed is. We don't have split PUD locks. -- Cheers, David / dhildenb