From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2DD92D3ABEA for ; Mon, 11 Nov 2024 18:31:34 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id B54AB6B0095; Mon, 11 Nov 2024 13:31:33 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id B03E76B0098; Mon, 11 Nov 2024 13:31:33 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 97DA16B0099; Mon, 11 Nov 2024 13:31:33 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 735ED6B0095 for ; Mon, 11 Nov 2024 13:31:33 -0500 (EST) Received: from smtpin25.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 1B796AABC9 for ; Mon, 11 Nov 2024 18:31:33 +0000 (UTC) X-FDA: 82774655712.25.7CF16DB Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf13.hostedemail.com (Postfix) with ESMTP id 91EE520022 for ; Mon, 11 Nov 2024 18:30:48 +0000 (UTC) Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=a5nFGTuB; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf13.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1731349828; a=rsa-sha256; cv=none; b=M2f5DfYYt39XrjQKae3+o05w4dXrBsZJIM4w50ONM0ALmx9SEx1pIJc+GQS8nNeJFkZlwH Uchy207loR8hALYsOrVQynjF7ti/El03NukemT4+FDTCehE7C2XEWsfATZOOOs+sYVWO5y dISZZsD87FlOOjDdhMaYVNgv93ybQvM= ARC-Authentication-Results: i=1; imf13.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=a5nFGTuB; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf13.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1731349828; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=Eo21+EnIRQQ2x3gyQarI5rgbsNGGXePICFJH8wlZVSQ=; b=NRGb+T4DtHT19uDMcI7VUSbGKtcqWyBK/nFmdBO9h1tFV2OPctVwkBLEZAh7P4SE9ytsgq 9Gz6xYHMMaBkkMj7ROrW2+lSvGWPjvpUPUw16uDJp95kBjaV6/79zeqJrL55ICuV6ZOOr+ E8ciOPSaHecmEBKtzSAOp2cAXAqj9BE= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1731349889; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=Eo21+EnIRQQ2x3gyQarI5rgbsNGGXePICFJH8wlZVSQ=; b=a5nFGTuBedDopSVSuHxAfEVGu7H+lJztpnmxLgtRA3T/qTkILiy6P7QxmTuHEYs7X2xCSq xnx6izXXK2RtLxb8evCRSv64pMH6cwbEeNgUGL8o6GDiTKxhRzS2tByBowJp/wTtGNypZH PobTnsGmrzZgjhZ/7nLbGNnFadHP4us= Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-120-zTfT0nCLPYSkvipNqTLnuQ-1; Mon, 11 Nov 2024 13:31:28 -0500 X-MC-Unique: zTfT0nCLPYSkvipNqTLnuQ-1 X-Mimecast-MFC-AGG-ID: zTfT0nCLPYSkvipNqTLnuQ Received: by mail-wm1-f70.google.com with SMTP id 5b1f17b1804b1-43159c07193so44983535e9.0 for ; Mon, 11 Nov 2024 10:31:28 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1731349887; x=1731954687; h=content-transfer-encoding:in-reply-to:organization:autocrypt:from :content-language:references:cc:to:subject:user-agent:mime-version :date:message-id:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=Eo21+EnIRQQ2x3gyQarI5rgbsNGGXePICFJH8wlZVSQ=; b=VJV7fA4LpxKOtBrZLsjWWBglDzLYkaOyzP+HRJpbDU/fcO+bPlhl20NduE+TUBjNit 5cOe93O0h2naDudIe7qKkbRsO6RKdyOzyQ+yQ1elkl2z6X0EryQERCFcBhcdnbFngHUk /m5csSpc2TDjmlj6CPCaXIAY3FdX3f/6NzRR8bM2327MBiwcv+3tjIlfmGX3UzdYFzyn 4mTZPlawOQVBu0E+w2g+Vcl3jZzVBYJHtxKowr2iUYX3v/eQyRz30hD+cFsI3JMTzuyA VgB1e6dzPvBNQRVpJI+g0WZk2dE3z++NqdGXBEjqOxQVuyfWk2hS192im42dZpUyNKs8 KMnQ== X-Forwarded-Encrypted: i=1; AJvYcCXizf7PenMRWXm1+J4bk5Htrv3tDibwcIkEoi8ZV1NnTn6O7o0wPa/9M9Mm+dUxd2/lznDu/bzMXg==@kvack.org X-Gm-Message-State: AOJu0YwooPdTbTm9DmWZ1O2Pu/b+9Mma1QwpzjZX0GHzbodloggKwufR k258I8EdwiMqSq7WiH/ilhOOZ1zFLq0OYPv2cPnA7wAX3TE2KZqye63z5vUVKUDsb9G4rkimdo5 faTyn5BjKcKgnlfZM7fvOSSzeAbpbpfPdBB5+sK0Ut3m17llA X-Received: by 2002:a05:600c:138a:b0:42c:bae0:f05f with SMTP id 5b1f17b1804b1-432b7505c2dmr147402365e9.13.1731349887178; Mon, 11 Nov 2024 10:31:27 -0800 (PST) X-Google-Smtp-Source: AGHT+IGiBvLMCzX5YDNiv3Xg0RmP53/cQ/3O9a7xsJWGNAQvZLpRa9hBI/rkowL2wPnaCuCbSuyDPw== X-Received: by 2002:a05:600c:138a:b0:42c:bae0:f05f with SMTP id 5b1f17b1804b1-432b7505c2dmr147402095e9.13.1731349886793; Mon, 11 Nov 2024 10:31:26 -0800 (PST) Received: from ?IPV6:2003:cb:c730:4300:18eb:6c63:a196:d3a2? (p200300cbc730430018eb6c63a196d3a2.dip0.t-ipconnect.de. [2003:cb:c730:4300:18eb:6c63:a196:d3a2]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-432aa5b5fc9sm218821265e9.3.2024.11.11.10.31.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 11 Nov 2024 10:31:26 -0800 (PST) Message-ID: Date: Mon, 11 Nov 2024 19:31:24 +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: p9trq36anXGrb91Q3C1fq2KlTHrg2-z3P96v67A2xfA_1731349887 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-Queue-Id: 91EE520022 X-Rspamd-Server: rspam01 X-Stat-Signature: hq3d11xqpekbs6yki51tpf6o959ipgkz X-HE-Tag: 1731349848-398858 X-HE-Meta: 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 zV79CSmO 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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 17:08, Yafang Shao wrote: > On Mon, Nov 11, 2024 at 11:05 PM 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. >> >> [...] >> >>> 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? > > This branch may also be triggered by other large folios that are not > necessarily order-9. Therefore, I’ve referred to it as a 'large folio' > rather than associating it specifically with MADV_HUGEPAGE. If we were > to handle only the MADV_HUGEPAGE case, we would proceed as outlined in > the initial RFC patch[0]. However, following Willy's recommendation, I > implemented it this way, as he likely has a deeper understanding of > the intended behavior. Sorry, but this code is getting quite confusing, especially with such misleading "large folio" comments. Even without MADV_HUGEPAGE we will be allocating large folios, as emphasized by Willy [1]. So the only thing MADV_HUGEPAGE controls is *which* large folios we allocate. .. as Willy says [2]: "We were only intending to breach the 'max' for the MADV_HUGE case, not for all cases." I have no idea how *anybody* should derive from the code here that we treat MADV_HUGEPAGE in a special way. Simply completely confusing. My interpretation of "I don't know if we should try to defend a stupid sysadmin against the consequences of their misconfiguration like this" means" would be "drop this patch and don't change anything". No changes to API, no confusing code. Maybe pr_info_once() when someone uses MADV_HUGEPAGE with such backends to tell the sysadmin that something stupid is happening ... [1] https://lore.kernel.org/linux-mm/ZyzV-RV0fpWABdWD@casper.infradead.org/ [2] https://lore.kernel.org/linux-mm/ZyxHc5Uukh47CO2R@casper.infradead.org/ -- Cheers, David / dhildenb