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 C43D5E77188 for ; Fri, 10 Jan 2025 21:00:25 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 54CA28D0002; Fri, 10 Jan 2025 16:00:25 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 4FC1F8D0001; Fri, 10 Jan 2025 16:00:25 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 34F098D0002; Fri, 10 Jan 2025 16:00:25 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 115D78D0001 for ; Fri, 10 Jan 2025 16:00:25 -0500 (EST) Received: from smtpin03.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 428CC1A0E42 for ; Fri, 10 Jan 2025 21:00:24 +0000 (UTC) X-FDA: 82992760368.03.9B0CC0D Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf22.hostedemail.com (Postfix) with ESMTP id 98849C0006 for ; Fri, 10 Jan 2025 21:00:21 +0000 (UTC) Authentication-Results: imf22.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b="HbfM1Hs/"; spf=pass (imf22.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1736542821; 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=J8959kPUFfZLBQMBHdBv1fGZ4buFB3gN6EGpnvIiwRQ=; b=AolKT2+mejtpKgw2U8de3szFsyjwW3kIu061QK8/EDaDDkb2EgtqSo90enFc3CC2lEo0Kx r83rONEVZ2AfYU1d6OIKKjZnsfO1uhtnJjY1NZaJ617Xn9xTA2wpYGJ0xJuCPQEWslsHyK A4iyjZDWWDXfkHb3U4Wxs+W3LdWr+4c= ARC-Authentication-Results: i=1; imf22.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b="HbfM1Hs/"; spf=pass (imf22.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1736542821; a=rsa-sha256; cv=none; b=SdGsM6pSYmS1SnEky4mWtsloIJmPdXrevHWdVMfOGCb5Zx0EZHv+42Heu8QGcrYFZsnPTK f6ozQk5wVXG9+WV4B9GoiJBOj7eRabwAJ941U4W+IhjbmisXTcR0cQZY8ZmsCtJxbiGk2+ sMIyyijx0wAVpvo6e/eyInZ6ixf9TDA= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1736542820; 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=J8959kPUFfZLBQMBHdBv1fGZ4buFB3gN6EGpnvIiwRQ=; b=HbfM1Hs/UqAXpxU0PH8U1LjmJa3OCsvnZGTuBcI6Z6BKOe0zfRXsQMf0H5i3V+H/IraEIb H9ENye+utMU9p8ThfNqrrF3Y5+K9zm0Es1f8O9d3ygnv18hXFLPW22GtRqZZn9/wpHnS2X U8nNAgrquX+LdM6HSvUsoBAc8TkipOg= 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-434-ru5SGTuTPgCqTYvwa8EBFA-1; Fri, 10 Jan 2025 16:00:12 -0500 X-MC-Unique: ru5SGTuTPgCqTYvwa8EBFA-1 X-Mimecast-MFC-AGG-ID: ru5SGTuTPgCqTYvwa8EBFA Received: by mail-wm1-f70.google.com with SMTP id 5b1f17b1804b1-4361eb83f46so20985375e9.3 for ; Fri, 10 Jan 2025 13:00:12 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1736542811; x=1737147611; h=content-transfer-encoding:in-reply-to:organization:autocrypt :content-language:from: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=J8959kPUFfZLBQMBHdBv1fGZ4buFB3gN6EGpnvIiwRQ=; b=p7QtDxZcsCzpCx7nmzPA+dlRAmZSHrnt6muroMCdMnIOzWVDKHqooK48yiPtWi68YQ OTzj/nkXzF2BIpKWwIBUiy4WROD7sCWaW9F93Q+rV3XskoMXRUxPGo6OAZ11LWR+tq6C PPN0DwMTC6kkT9Q+I2DCW24LZmmZsoocjoNGUMYpgcHvoqTAq30WwQ+WIcdiaXCpQjy+ vJZWKJuYpC6b0DKNEeKd/RaM3EZxYwDlFSsEBCwzQZ1yRnfIpCjO+VzsLgfCiAXyPjZp q0Z5oz3xnmXTdc3Z/cwB9aQMoOEjbVMQ+Llz/Xs1s5gayRj90V7iO9TdVyOpwl3dM7J5 IyQw== X-Forwarded-Encrypted: i=1; AJvYcCXv73/vIhkValrmhVQezQ7j5FWpjoVfwXcjU7fi56565rL33J2Rht0B+Yh6n7IQLN7Ch8yVnKBqEg==@kvack.org X-Gm-Message-State: AOJu0YzfZR/uwVXwrae1VrZmcGkRVSH2o7xjxkENByB4NSD5PCFKhpqY t2jiBwioB8RrdxQJEqt02qRSMg5gpyz1oer8bXyCBQBAGvscpXtp+GUiwHk2XQNZ3lLM/+nbIOW 4Zzy3yYcts6ASE/PtV4EhyrnDCeTVnK4ADP/f9pL5sXvunTJG X-Gm-Gg: ASbGncvdJUzZN2c0Z5seunjkK9M6L/PBqSHhORD/gwUsqrj7gkPkEEMJU3g59kYKVrH vt9YNz7hovYVAcp/5CmNkZO70ImSv7Kiw4MeX3Iwef9fYQ4hfEkq4gZEGqF5/hRHH5b46jp1tVR HvYhou+Ej6KmbMa3K2WNbsksNs7/swIxyzUGGHC/M1tjWAChSBZzmFev/AWE/6KJ0yx6A4j5ci8 eEiDC2PFrdllAh0HnW+gFeJ/sOZ+wgYV+V7xHrlBNDkF/DopZzC6bWnd29iuJB4HnBkB8+D16os l5a9SUHyJSFaE37Hlarc3S/9gz96O5tgkkqgLTsEGE/ba7cuLP3ZnH/7uxI3yokNbEAmPM0WNZU hS1xKa/Cg X-Received: by 2002:a05:6000:402a:b0:38a:418e:1171 with SMTP id ffacd0b85a97d-38a8733063dmr10695849f8f.37.1736542811258; Fri, 10 Jan 2025 13:00:11 -0800 (PST) X-Google-Smtp-Source: AGHT+IGM4OmO1WZ/aPg6xuVDjy8ByYrrVozhZ9CL4TDkPULchrT1u3C/ZMp/IAZjkr1ST3cgAQkPRQ== X-Received: by 2002:a05:6000:402a:b0:38a:418e:1171 with SMTP id ffacd0b85a97d-38a8733063dmr10695827f8f.37.1736542810888; Fri, 10 Jan 2025 13:00:10 -0800 (PST) Received: from ?IPV6:2003:cb:c708:e100:4f41:ff29:a59f:8c7a? (p200300cbc708e1004f41ff29a59f8c7a.dip0.t-ipconnect.de. [2003:cb:c708:e100:4f41:ff29:a59f:8c7a]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38a8e37d0b1sm5492880f8f.12.2025.01.10.13.00.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 10 Jan 2025 13:00:10 -0800 (PST) Message-ID: Date: Fri, 10 Jan 2025 22:00:08 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 4/5] mm/migrate: skip migrating folios under writeback with AS_WRITEBACK_INDETERMINATE mappings To: Jeff Layton , Shakeel Butt , Miklos Szeredi Cc: Joanne Koong , Bernd Schubert , Zi Yan , linux-fsdevel@vger.kernel.org, jefflexu@linux.alibaba.com, josef@toxicpanda.com, linux-mm@kvack.org, kernel-team@meta.com, Matthew Wilcox , Oscar Salvador , Michal Hocko References: <0ed5241e-10af-43ee-baaf-87a5b4dc9694@redhat.com> <446704ab-434e-45ac-a062-45fef78815e4@redhat.com> <791d4056-cac1-4477-a8e3-3a2392ed34db@redhat.com> <153c5a4f08daf60e1bbbdde02975392dc608cfdf.camel@kernel.org> <47fff939fc1fb3153af5b129be600a018c8485e9.camel@kernel.org> 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: <47fff939fc1fb3153af5b129be600a018c8485e9.camel@kernel.org> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: ZsI3Fv1E9udWFOwEH2KsMDUYuUn1FNm347IjMKgDMRo_1736542811 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 98849C0006 X-Rspam-User: X-Stat-Signature: 5wxyzf5rmwnynj5teo3jyxjrknagssxo X-HE-Tag: 1736542821-494020 X-HE-Meta: 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 KeC6gfjH NoiBMQc2MRqdVCXkFwANHrguaL2W0uBwvvkgLvTiT0HBoaFS6WlrSasKu7RT8z1360pMbwCdwZfJmrb/LQ3pFEQUVp0JuPBmIAgW3Rqzb4XYYCMarGTh1pt4H771/Tk924qjPBMoHVl7UL4LDqEDvnu33x8+6IstyoZdn8PqTEM0ZTZV3cIc2+SLQO9Zh2PfJ9QK4Wjwja3Ebc1WOufeEHrvJaELAVabkpx62ZuO0jGeMglxLDqmbyCk2OBvNcs+B2a6kw/10qg+58n7ezVhvOOqwW1le+wqF4546V6YDEQq90m9WqbRAlW1jKHwLveZCLWSsZ9eJOFdtaGMnuLzGcQx3B+a2n871n2SYCYgSB+YSa+9oMVKxhBQ//yD3K7J/l26jXcoujUf5/txGXLAgxm+/KZX4J+t6xHp5Yzh0LTsVb6OjMMqwHHX0k79t3siUA42rk13yTFvah3TvirfAHt1uug== 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 10.01.25 21:43, Jeff Layton wrote: > On Fri, 2025-01-10 at 21:20 +0100, David Hildenbrand wrote: >> On 10.01.25 21:16, Jeff Layton wrote: >>> On Tue, 2025-01-07 at 09:34 +0100, David Hildenbrand wrote: >>>> On 06.01.25 19:17, Shakeel Butt wrote: >>>>> On Mon, Jan 06, 2025 at 11:19:42AM +0100, Miklos Szeredi wrote: >>>>>> On Fri, 3 Jan 2025 at 21:31, David Hildenbrand wrote: >>>>>>> In any case, having movable pages be turned unmovable due to persistent >>>>>>> writaback is something that must be fixed, not worked around. Likely a >>>>>>> good topic for LSF/MM. >>>>>> >>>>>> Yes, this seems a good cross fs-mm topic. >>>>>> >>>>>> So the issue discussed here is that movable pages used for fuse >>>>>> page-cache cause a problems when memory needs to be compacted. The >>>>>> problem is either that >>>>>> >>>>>> - the page is skipped, leaving the physical memory block unmovable >>>>>> >>>>>> - the compaction is blocked for an unbounded time >>>>>> >>>>>> While the new AS_WRITEBACK_INDETERMINATE could potentially make things >>>>>> worse, the same thing happens on readahead, since the new page can be >>>>>> locked for an indeterminate amount of time, which can also block >>>>>> compaction, right? >>>> >>>> Yes, as memory hotplug + virtio-mem maintainer my bigger concern is >>>> these pages residing in ZONE_MOVABLE / MIGRATE_CMA areas where there >>>> *must not be unmovable pages ever*. Not triggered by an untrusted >>>> source, not triggered by an trusted source. >>>> >>>> It's a violation of core-mm principles. >>>> >>>> Even if we have a timeout of 60s, making things like alloc_contig_page() >>>> wait for that long on writeback is broken and needs to be fixed. >>>> >>>> And the fix is not to skip these pages, that's a workaround. >>>> >>>> I'm hoping I can find an easy way to trigger this also with NFS. >>>> >>> >>> I imagine that you can just open a file and start writing to it, pull >>> the plug on the NFS server, and then issue a fsync or something to >>> ensure some writeback occurs. >> >> Yes, that's the plan, thanks! >> >>> >>> Any dirty pagecache folios should be stuck in writeback at that point. >>> The NFS client is also very patient about waiting for the server to >>> come back, so it should stay that way indefinitely. >> >> Yes, however the default timeout for UDP is fairly small (for TCP >> certainly much longer). So one thing I'd like to understand what that >> "cancel writeback -> redirty folio" on timeout does, and when it >> actually triggers with TCP vs UDP timeouts. >> > > > The lifetime of the pagecache pages is not at all related to the socket > lifetimes. IOW, the client can completely lose the connection to the > server and the page will just stay dirty until the connection can be > reestablished and the server responds. Right. It cannot get reclaimed while that is the case. > > The exception here is if you mount with "-o soft" in which case, an RPC > request will time out with an error after a major RPC timeout (usually > after a minute or so). See nfs(5) for the gory details of timeouts and > retransmission. The default is "-o hard" since that's necessary for > data-integrity in the face of spotty network connections. > > Once a soft mount has a writeback RPC time out, the folio is marked > clean and a writeback error is set on the mapping, so that fsync() will > return an error. I assume that's the code I stumbled over in nfs_page_async_flush(), where we end up calling folio_redirty_for_writepage() + nfs_redirty_request(), unless we run into a fatal error; in that case, we end up in nfs_write_error() where we set the mapping error and stop writeback using nfs_page_end_writeback(). -- Cheers, David / dhildenb