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([2a01:599:915:8911:b13f:d972:e237:7fe2]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a099b178absm14075606f8f.97.2025.05.06.07.24.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 06 May 2025 07:24:50 -0700 (PDT) Message-ID: <5ea287f0-24cb-4ad4-8448-6e397fbf1ec8@redhat.com> Date: Tue, 6 May 2025 16:24:48 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v4 4/5] mm/readahead: Store folio order in struct file_ra_state To: Ryan Roberts , Andrew Morton , "Matthew Wilcox (Oracle)" , Alexander Viro , Christian Brauner , Jan Kara , Dave Chinner , Catalin Marinas , Will Deacon , Kalesh Singh , Zi Yan Cc: 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> <20250430145920.3748738-5-ryan.roberts@arm.com> <2b1ea3d9-6c9b-4700-ae21-5f65565a995a@arm.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: <2b1ea3d9-6c9b-4700-ae21-5f65565a995a@arm.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: BB5Ky6Akg73RQGaUUWGP11r_D3YT3VbtH2mfPFc1-Dw_1746541492 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250506_072457_272784_1EBFE9C2 X-CRM114-Status: GOOD ( 16.30 ) 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 06.05.25 12:03, Ryan Roberts wrote: > On 05/05/2025 11:08, David Hildenbrand wrote: >> On 30.04.25 16:59, Ryan Roberts wrote: >>> Previously the folio order of the previous readahead request was >>> inferred from the folio who's readahead marker was hit. But due to the >>> way we have to round to non-natural boundaries sometimes, this first >>> folio in the readahead block is often smaller than the preferred order >>> for that request. This means that for cases where the initial sync >>> readahead is poorly aligned, the folio order will ramp up much more >>> slowly. >>> >>> So instead, let's store the order in struct file_ra_state so we are not >>> affected by any required alignment. We previously made enough room in >>> the struct for a 16 order field. This should be plenty big enough since >>> we are limited to MAX_PAGECACHE_ORDER anyway, which is certainly never >>> larger than ~20. >>> >>> Since we now pass order in struct file_ra_state, page_cache_ra_order() >>> no longer needs it's new_order parameter, so let's remove that. >>> >>> Worked example: >>> >>> Here we are touching pages 17-256 sequentially just as we did in the >>> previous commit, but now that we are remembering the preferred order >>> explicitly, we no longer have the slow ramp up problem. Note >>> specifically that we no longer have 2 rounds (2x ~128K) of order-2 >>> folios: >>> >>> TYPE    STARTOFFS     ENDOFFS        SIZE  STARTPG    ENDPG   NRPG  ORDER  RA >>> -----  ----------  ----------  ----------  -------  -------  -----  -----  -- >>> HOLE   0x00000000  0x00001000        4096        0        1      1 >>> 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  0x00021000        4096       32       33      1      0 >>> FOLIO  0x00021000  0x00022000        4096       33       34      1      0 >>> FOLIO  0x00022000  0x00024000        8192       34       36      2      1 >>> 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 >>> FOLIO  0x000e0000  0x00100000      131072      224      256     32      5 >>> FOLIO  0x00100000  0x00120000      131072      256      288     32      5 >>> FOLIO  0x00120000  0x00140000      131072      288      320     32      5  Y >>> HOLE   0x00140000  0x00800000     7077888      320     2048   1728 >>> >>> Signed-off-by: Ryan Roberts >>> --- >>>   include/linux/fs.h |  2 ++ >>>   mm/filemap.c       |  6 ++++-- >>>   mm/internal.h      |  3 +-- >>>   mm/readahead.c     | 18 +++++++++++------- >>>   4 files changed, 18 insertions(+), 11 deletions(-) >>> >>> diff --git a/include/linux/fs.h b/include/linux/fs.h >>> index 44362bef0010..cde482a7270a 100644 >>> --- a/include/linux/fs.h >>> +++ b/include/linux/fs.h >>> @@ -1031,6 +1031,7 @@ struct fown_struct { >>>    *      and so were/are genuinely "ahead".  Start next readahead when >>>    *      the first of these pages is accessed. >>>    * @ra_pages: Maximum size of a readahead request, copied from the bdi. >>> + * @order: Preferred folio order used for most recent readahead. >> >> Looking at other members, and how it relates to the other members, should we >> call this something like "ra_prev_order" / "prev_ra_order" to distinguish it >> from !ra members and indicate the "most recent" semantics similar to "prev_pos"? > > As you know, I'm crap at naming, but... > > start, size, async_size and order make up the parameters for the "most recent" > readahead request. Where "most recent" includes "current" once passed into > page_cache_ra_order(). The others don't include "ra" or "prev" in their name so > wasn't sure it was necessary here. > > ra_pages is a bit different; that's not part of the request, it's a (dynamic) > ceiling to use when creating requests. > > Personally I'd leave it as is, but no strong opinion. I'm fine with it staying that way; I was merely trying to make sense of it all ... ... maybe a better description of the parameters might make the semantics easier to grasp. ""most recent" includes "current" once passed into page_cache_ra_order()" is *really* hard to digest :) > >> >> Just a thought while digging through this patch ... >> >> ... >> >>> --- a/mm/filemap.c >>> +++ b/mm/filemap.c >>> @@ -3222,7 +3222,8 @@ static struct file *do_sync_mmap_readahead(struct >>> vm_fault *vmf) >>>           if (!(vm_flags & VM_RAND_READ)) >>>               ra->size *= 2; >>>           ra->async_size = HPAGE_PMD_NR; >>> -        page_cache_ra_order(&ractl, ra, HPAGE_PMD_ORDER); >>> +        ra->order = HPAGE_PMD_ORDER; >>> +        page_cache_ra_order(&ractl, ra); >>>           return fpin; >>>       } >>>   #endif >>> @@ -3258,8 +3259,9 @@ static struct file *do_sync_mmap_readahead(struct >>> vm_fault *vmf) >>>       ra->start = max_t(long, 0, vmf->pgoff - ra->ra_pages / 2); >>>       ra->size = ra->ra_pages; >>>       ra->async_size = ra->ra_pages / 4; >>> +    ra->order = 0; >>>       ractl._index = ra->start; >>> -    page_cache_ra_order(&ractl, ra, 0); >>> +    page_cache_ra_order(&ractl, ra); >>>       return fpin; >>>   } >> >> Why not let page_cache_ra_order() consume the order and update ra->order (or >> however it will be called :) ) internally? > > You mean continue to pass new_order as a parameter to page_cache_ra_order()? The > reason I did it the way I'm doing it is because I thought it would be weird for > the caller of page_cache_ra_order() to set up all the parameters (start, size, > async_size) of the request except for order... Agreed. As above, I think we might do better with the description of these parameters in general ... or even document how page_cache_ra_order() acts on these inputs? -- Cheers, David / dhildenb