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[2003:cb:c730:4300:18eb:6c63:a196:d3a2]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-381ed97ce0fsm13072723f8f.33.2024.11.11.07.05.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 11 Nov 2024 07:05:50 -0800 (PST) Message-ID: Date: Mon, 11 Nov 2024 16:05:49 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm/readahead: Fix large folio support in async readahead 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> 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: Z-ShXniyBvENFfcPT6vJ-blCXo0hH3APzA0Zv-qfWY4_1731337552 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 323CE100033 X-Stat-Signature: mcjwd9a54ouup1do6tqq9hywdiwddahi X-HE-Tag: 1731337478-740149 X-HE-Meta: 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 w5p56ed7 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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 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. [...] > Perhaps a more straightforward solution would be to implement it > directly at the callsite, as demonstrated below? Likely something into this direction might be better, but Willy is the expert that code. > > diff --git a/mm/readahead.c b/mm/readahead.c > index 3dc6c7a128dd..187efae95b02 100644 > --- a/mm/readahead.c > +++ b/mm/readahead.c > @@ -642,7 +642,11 @@ void page_cache_async_ra(struct readahead_control *ractl, > 1UL << order); > if (index == expected) { > ra->start += ra->size; > - ra->size = get_next_ra_size(ra, max_pages); > + /* > + * Allow the actual size to exceed the readahead window for a > + * large folio. "a large folio" -> "with MADV_HUGEPAGE" ? Or can this be hit on different paths that are not covered in the patch description? -- Cheers, David / dhildenb