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[2003:cb:c73d:2400:3be1:a856:724c:fd29]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-441b89cc50esm132057425e9.8.2025.05.05.03.25.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 05 May 2025 03:25:37 -0700 (PDT) Message-ID: Date: Mon, 5 May 2025 12:25:36 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v4 1/5] mm/readahead: Honour new_order in page_cache_ra_order() To: Jan Kara Cc: Ryan Roberts , Andrew Morton , "Matthew Wilcox (Oracle)" , Alexander Viro , Christian Brauner , Dave Chinner , Catalin Marinas , Will Deacon , Kalesh Singh , Zi Yan , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org References: <20250430145920.3748738-1-ryan.roberts@arm.com> <20250430145920.3748738-2-ryan.roberts@arm.com> <48b4aa79-943b-46bc-ac24-604fdf998566@redhat.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: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: zYZvHba8OiPOCgTKBkl2tYUGuP6Q3Div9k8SaDM_SKA_1746440738 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250505_032544_220984_D2535A97 X-CRM114-Status: GOOD ( 17.88 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 05.05.25 12:09, Jan Kara wrote: > On Mon 05-05-25 11:51:43, David Hildenbrand wrote: >> On 30.04.25 16:59, Ryan Roberts wrote: >>> page_cache_ra_order() takes a parameter called new_order, which is >>> intended to express the preferred order of the folios that will be >>> allocated for the readahead operation. Most callers indeed call this >>> with their preferred new order. But page_cache_async_ra() calls it with >>> the preferred order of the previous readahead request (actually the >>> order of the folio that had the readahead marker, which may be smaller >>> when alignment comes into play). >>> >>> And despite the parameter name, page_cache_ra_order() always treats it >>> at the old order, adding 2 to it on entry. As a result, a cold readahead >>> always starts with order-2 folios. >>> >>> Let's fix this behaviour by always passing in the *new* order. >>> >>> Worked example: >>> >>> Prior to the change, mmaping an 8MB file and touching each page >>> sequentially, resulted in the following, where we start with order-2 >>> folios for the first 128K then ramp up to order-4 for the next 128K, >>> then get clamped to order-5 for the rest of the file because pa_pages is >>> limited to 128K: >>> >>> TYPE STARTOFFS ENDOFFS SIZE STARTPG ENDPG NRPG ORDER >>> ----- ---------- ---------- --------- ------- ------- ----- ----- >>> FOLIO 0x00000000 0x00004000 16384 0 4 4 2 >>> FOLIO 0x00004000 0x00008000 16384 4 8 4 2 >>> FOLIO 0x00008000 0x0000c000 16384 8 12 4 2 >>> FOLIO 0x0000c000 0x00010000 16384 12 16 4 2 >>> FOLIO 0x00010000 0x00014000 16384 16 20 4 2 >>> FOLIO 0x00014000 0x00018000 16384 20 24 4 2 >>> FOLIO 0x00018000 0x0001c000 16384 24 28 4 2 >>> FOLIO 0x0001c000 0x00020000 16384 28 32 4 2 >>> FOLIO 0x00020000 0x00030000 65536 32 48 16 4 >>> FOLIO 0x00030000 0x00040000 65536 48 64 16 4 >>> FOLIO 0x00040000 0x00060000 131072 64 96 32 5 >>> FOLIO 0x00060000 0x00080000 131072 96 128 32 5 >>> FOLIO 0x00080000 0x000a0000 131072 128 160 32 5 >>> FOLIO 0x000a0000 0x000c0000 131072 160 192 32 5 >> >> Interesting, I would have thought we'd ramp up earlier. >> >>> ... >>> >>> After the change, the same operation results in the first 128K being >>> order-0, then we start ramping up to order-2, -4, and finally get >>> clamped at order-5: >>> >>> TYPE STARTOFFS ENDOFFS SIZE STARTPG ENDPG NRPG ORDER >>> ----- ---------- ---------- --------- ------- ------- ----- ----- >>> FOLIO 0x00000000 0x00001000 4096 0 1 1 0 >>> FOLIO 0x00001000 0x00002000 4096 1 2 1 0 >>> FOLIO 0x00002000 0x00003000 4096 2 3 1 0 >>> FOLIO 0x00003000 0x00004000 4096 3 4 1 0 >>> FOLIO 0x00004000 0x00005000 4096 4 5 1 0 >>> FOLIO 0x00005000 0x00006000 4096 5 6 1 0 >>> FOLIO 0x00006000 0x00007000 4096 6 7 1 0 >>> FOLIO 0x00007000 0x00008000 4096 7 8 1 0 >>> FOLIO 0x00008000 0x00009000 4096 8 9 1 0 >>> FOLIO 0x00009000 0x0000a000 4096 9 10 1 0 >>> FOLIO 0x0000a000 0x0000b000 4096 10 11 1 0 >>> FOLIO 0x0000b000 0x0000c000 4096 11 12 1 0 >>> FOLIO 0x0000c000 0x0000d000 4096 12 13 1 0 >>> FOLIO 0x0000d000 0x0000e000 4096 13 14 1 0 >>> FOLIO 0x0000e000 0x0000f000 4096 14 15 1 0 >>> FOLIO 0x0000f000 0x00010000 4096 15 16 1 0 >>> FOLIO 0x00010000 0x00011000 4096 16 17 1 0 >>> FOLIO 0x00011000 0x00012000 4096 17 18 1 0 >>> FOLIO 0x00012000 0x00013000 4096 18 19 1 0 >>> FOLIO 0x00013000 0x00014000 4096 19 20 1 0 >>> FOLIO 0x00014000 0x00015000 4096 20 21 1 0 >>> FOLIO 0x00015000 0x00016000 4096 21 22 1 0 >>> FOLIO 0x00016000 0x00017000 4096 22 23 1 0 >>> FOLIO 0x00017000 0x00018000 4096 23 24 1 0 >>> FOLIO 0x00018000 0x00019000 4096 24 25 1 0 >>> FOLIO 0x00019000 0x0001a000 4096 25 26 1 0 >>> FOLIO 0x0001a000 0x0001b000 4096 26 27 1 0 >>> FOLIO 0x0001b000 0x0001c000 4096 27 28 1 0 >>> FOLIO 0x0001c000 0x0001d000 4096 28 29 1 0 >>> FOLIO 0x0001d000 0x0001e000 4096 29 30 1 0 >>> FOLIO 0x0001e000 0x0001f000 4096 30 31 1 0 >>> FOLIO 0x0001f000 0x00020000 4096 31 32 1 0 >>> FOLIO 0x00020000 0x00024000 16384 32 36 4 2 >>> FOLIO 0x00024000 0x00028000 16384 36 40 4 2 >>> FOLIO 0x00028000 0x0002c000 16384 40 44 4 2 >>> FOLIO 0x0002c000 0x00030000 16384 44 48 4 2 >>> FOLIO 0x00030000 0x00034000 16384 48 52 4 2 >>> FOLIO 0x00034000 0x00038000 16384 52 56 4 2 >>> FOLIO 0x00038000 0x0003c000 16384 56 60 4 2 >>> FOLIO 0x0003c000 0x00040000 16384 60 64 4 2 >>> FOLIO 0x00040000 0x00050000 65536 64 80 16 4 >>> FOLIO 0x00050000 0x00060000 65536 80 96 16 4 >>> FOLIO 0x00060000 0x00080000 131072 96 128 32 5 >>> FOLIO 0x00080000 0x000a0000 131072 128 160 32 5 >>> FOLIO 0x000a0000 0x000c0000 131072 160 192 32 5 >>> FOLIO 0x000c0000 0x000e0000 131072 192 224 32 5 >> >> Similar here, do you know why we don't ramp up earlier. Allocating that many >> order-0 + order-2 pages looks a bit suboptimal to me for a sequential read. > > Note that this is reading through mmap using the mmap readahead code. If > you use standard read(2), the readahead window starts small as well and > ramps us along with the desired order so we don't allocate that many small > order pages in that case. Ah, thanks for that information! :) -- Cheers, David / dhildenb