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[2003:cb:c730:4300:18eb:6c63:a196:d3a2]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-432bc472a48sm65206655e9.0.2024.11.11.07.26.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 11 Nov 2024 07:26:12 -0800 (PST) Message-ID: Date: Mon, 11 Nov 2024 16:26:11 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm/readahead: Fix large folio support in async readahead From: David Hildenbrand To: Yafang Shao Cc: willy@infradead.org, akpm@linux-foundation.org, linux-mm@kvack.org, stable@vger.kernel.org References: <20241108141710.9721-1-laoar.shao@gmail.com> <85cfc467-320f-4388-b027-2cbad85dfbed@redhat.com> 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: KImLoWzEbIljHeK2Kgm6tfmCBLWNedNecgwivKjcG28_1731338774 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Stat-Signature: t5pfnxgfnwwg7bseegkawirusrwthfzc X-Rspam-User: X-Rspamd-Queue-Id: E72E116002B X-Rspamd-Server: rspam02 X-HE-Tag: 1731338749-303246 X-HE-Meta: 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 C24lfeRZ 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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 11.11.24 16:05, David Hildenbrand wrote: > On 11.11.24 15:28, Yafang Shao wrote: >> On Mon, Nov 11, 2024 at 6:33 PM David Hildenbrand wrote: >>> >>> On 08.11.24 15:17, Yafang Shao wrote: >>>> When testing large folio support with XFS on our servers, we observed that >>>> only a few large folios are mapped when reading large files via mmap. >>>> After a thorough analysis, I identified it was caused by the >>>> `/sys/block/*/queue/read_ahead_kb` setting. On our test servers, this >>>> parameter is set to 128KB. After I tune it to 2MB, the large folio can >>>> work as expected. However, I believe the large folio behavior should not be >>>> dependent on the value of read_ahead_kb. It would be more robust if the >>>> kernel can automatically adopt to it. >>> >>> Now I am extremely confused. >>> >>> Documentation/ABI/stable/sysfs-block: >>> >>> "[RW] Maximum number of kilobytes to read-ahead for filesystems on this >>> block device." >>> >>> >>> So, with your patch, will we also be changing the readahead size to >>> exceed that, or simply allocate larger folios and not exceeding the >>> readahead size (e.g., leaving them partially non-filled)? >> >> Exceeding the readahead size for the MADV_HUGEPAGE case is >> straightforward; this is what the current patch accomplishes. >> > > Okay, so this only applies with MADV_HUGEPAGE I assume. Likely we should > also make that clearer in the subject. > > mm/readahead: allow exceeding configured read_ahead_kb with MADV_HUGEPAGE > > > If this is really a fix, especially one that deserves CC-stable, I > cannot tell. Willy is the obvious expert :) > >>> >>> If you're also changing the readahead behavior to exceed the >>> configuration parameter it would sound to me like "I am pushing the >>> brake pedal and my care brakes; fix the brakes to adopt whether to brake >>> automatically" :) >>> >>> Likely I am missing something here, and how the read_ahead_kb parameter >>> is used after your patch. >> >> The read_ahead_kb parameter continues to function for >> non-MADV_HUGEPAGE scenarios, whereas special handling is required for >> the MADV_HUGEPAGE case. It appears that we ought to update the >> Documentation/ABI/stable/sysfs-block to reflect the changes related to >> large folios, correct? > > Yes, how it related to MADV_HUGEPAGE. I would assume that it would get > ignored, but ... > > ... staring at get_next_ra_size(), it's not quite ignored, because we > still us it as a baseline to detect how much we want to bump up the > limit when the requested size is small? (*2 vs *4 etc) :/ > > So the semantics are really starting to get weird, unless I am missing > something important. Likely what I am missing is that the value of get_next_ra_size() will never be relevant in that case. I assume the following would end up doing the same: iff --git a/mm/readahead.c b/mm/readahead.c index 475d2940a1edb..cc7f883f83d86 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -668,7 +668,12 @@ void page_cache_async_ra(struct readahead_control *ractl, ra->start = start; ra->size = start - index; /* old async_size */ ra->size += req_count; - ra->size = get_next_ra_size(ra, max_pages); + /* + * Allow the actual size to exceed the readahead window for + * MADV_HUGEPAGE. + */ + if (ra->size < max_pages) + ra->size = get_next_ra_size(ra, max_pages); ra->async_size = ra->size; readit: ractl->_index = ra->start; So maybe it should just be in get_next_ra_size() where we clarify what "max_pages" means and why we simply decide to ignore the value ... -- Cheers, David / dhildenb