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 6A6B3C7115A for ; Wed, 18 Jun 2025 11:54:31 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 0B57B6B0095; Wed, 18 Jun 2025 07:54:31 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 08D9D6B0096; Wed, 18 Jun 2025 07:54:31 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id EBE4E6B0098; Wed, 18 Jun 2025 07:54:30 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id DCF506B0095 for ; Wed, 18 Jun 2025 07:54:30 -0400 (EDT) Received: from smtpin29.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id B52BB1D817C for ; Wed, 18 Jun 2025 11:54:30 +0000 (UTC) X-FDA: 83568363900.29.8BFA24D Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf18.hostedemail.com (Postfix) with ESMTP id 165361C0007 for ; Wed, 18 Jun 2025 11:54:27 +0000 (UTC) Authentication-Results: imf18.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b="dGMKI/wf"; dmarc=pass (policy=quarantine) header.from=redhat.com; spf=pass (imf18.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=1750247668; a=rsa-sha256; cv=none; b=fpgdtYfQz5dsoSMGOYf0ciN7ZPxWQlUMqwnVLXAilIG8VDYvy7DmHJBsneZF8YBOZCvBwv p3SSSFhyBkubr6kkRCvH3fo9DmIqiaILhYOdep9t7LsQIg9X9IJQ/hrIKSlEjwjQk3ZIau musSObVz8xgfVM9HnsXiH7vWTF8Ss2Y= ARC-Authentication-Results: i=1; imf18.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b="dGMKI/wf"; dmarc=pass (policy=quarantine) header.from=redhat.com; spf=pass (imf18.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=1750247668; 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=DOpGfej+wKG1VgbU16FOUc0UnKXyUIhgPDNTdOtNZD0=; b=GyyEb9xnsIAxUvwe6M3K/TfuZlhjhf3cCAxe8YM03+9dmTyzpssxpIkqu9s711sB9LOZa1 nPY93PBbV7V4KPv+VHFVQvOK3Zpif1D48OL2KKGypIj6NSE6yvy0JFw3xKUfmJQMDW8rCZ kyTXHlxMObr82GdLdUK2KCT+NnXujAk= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1750247667; 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=DOpGfej+wKG1VgbU16FOUc0UnKXyUIhgPDNTdOtNZD0=; b=dGMKI/wfKJh7QLEIuOP30HdyY/lsZYsVN1Z5SoGqPgpRpNwRi2/sJdjwftWJPDaunMQslx y8fyRHwkSBMuSxJr3GXUDsYVE8ueU2mleejjAmo2odNfW02jNWfGr6Eo/sXARU55abp0ad Ij4EwSoXwASSIlxEyj8G/Da6gtRLhmE= Received: from mail-wr1-f72.google.com (mail-wr1-f72.google.com [209.85.221.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-274-6AS96JcYMl235J2ZMWRmeg-1; Wed, 18 Jun 2025 07:54:24 -0400 X-MC-Unique: 6AS96JcYMl235J2ZMWRmeg-1 X-Mimecast-MFC-AGG-ID: 6AS96JcYMl235J2ZMWRmeg_1750247663 Received: by mail-wr1-f72.google.com with SMTP id ffacd0b85a97d-3a503f28b09so366398f8f.0 for ; Wed, 18 Jun 2025 04:54:24 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1750247663; x=1750852463; 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=DOpGfej+wKG1VgbU16FOUc0UnKXyUIhgPDNTdOtNZD0=; b=jQ7sETXRLQYo/eTNrr8mLCrNQewUpgBt4yD0Fu2T4n+GPg1h8LJip6R+ydz5M5maUL YsLBKpPRMuLUpKabNGqf+889oaL5lcdmbKQunvHsk3Mm5tRNxXrf6VYrPfwyX0qOFDio zo2iYUcEkFDINgrA9NKE2ZWYdhH/IN9rW4IwTpld4Pt7Dg7bRYOt5Yn6mQ4Md5PbAcdS rh9IVZRcScNZuvCaGc8+GZJT5cphpfuTQJTsFluzsoYAt7B1iC3+Q8DfjAtdQjR9U1Xu Mz6IPt274DAaRgjaGQDgZapXhQ7avRb93kjUd+jv3NZrHnm3ms9sx4Vd0Il9iIeqaqWl OFqw== X-Forwarded-Encrypted: i=1; AJvYcCWbbIXW7SDQv+PZzEpxGznZ4Z+ffviPcsNzmfw0T5Vasj+9P0a1Ix72fmpyzH/0JPfr0SjNji6Wew==@kvack.org X-Gm-Message-State: AOJu0YxT8YTc4j4VsFNxe95+WxiF1OoebQhfIhdGYv0azFZNxCDyTCZQ CfDw6xmyHQNCXa7DAAah57WiUxZLP6EIPnbtUyYrKtpUWlzMbDDETJ/D34X8Lkg9Rw8JCRRbckj vmMjmJ5TWVgHHScVtyS2ptgLWd9wGgtBe9vcDvrFxnQ7aQMRti2ig X-Gm-Gg: ASbGncuDoxz5JmrxPnpzR00EPaCEV/03J94D4h2O6uqCcMGvT8ZLak6cPhMH0p5hiaW r/h5XD6c6tfGvHr09E6zZLe4qjgSMDlTNShNlKqI8wou7T6Jat8XqXEC5PrEVG5oXI7sUR4+J9d 0muESwaZVTnwsBsJbNZX3AuTe0j9RqJOJZyEBV3dDeeGUPMz6nd3rBRTAB8O9sRl26isrSQFbxn nuDC72f40Wpvmg/dISBud0oPWgcoIi0NfUWr1b3bL4+Iny7+IE0vvmtJ5r5KZPIL2KlIcK4L4wk rbb2eIG9V9jAI8Prc+VSBs8f+Er7hayBbCUfJpjwFPRizpd8gnraZDSqsVzcfhTHXP0WKkgB1co fpXCGF5zLrooExyaJXHzI9Srq+6hSsG4bufM0GIh8REihBwc= X-Received: by 2002:a05:6000:2912:b0:3a4:f70e:bc25 with SMTP id ffacd0b85a97d-3a58e27010emr2270299f8f.27.1750247663127; Wed, 18 Jun 2025 04:54:23 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFuRFbotFuND835d6U8YkfRTmqYzSB0JPy+NFDmJbKVME80bESVN6r6F3K7HXj+5H5asC46Dg== X-Received: by 2002:a05:6000:2912:b0:3a4:f70e:bc25 with SMTP id ffacd0b85a97d-3a58e27010emr2270258f8f.27.1750247662637; Wed, 18 Jun 2025 04:54:22 -0700 (PDT) Received: from ?IPV6:2003:d8:2f2d:2400:4052:3b5:fff9:4ed0? (p200300d82f2d2400405203b5fff94ed0.dip0.t-ipconnect.de. [2003:d8:2f2d:2400:4052:3b5:fff9:4ed0]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a568b5c372sm16341652f8f.89.2025.06.18.04.54.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 18 Jun 2025 04:54:22 -0700 (PDT) Message-ID: <345a04ad-cf25-4af5-802a-bc8826d37b19@redhat.com> Date: Wed, 18 Jun 2025 13:54:20 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] PM: Optionally block user fork during freeze to improve performance To: Zihuan Zhang , Michal Hocko Cc: Peter Zijlstra , rafael@kernel.org, len.brown@intel.com, pavel@kernel.org, kees@kernel.org, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20250606062502.19607-1-zhangzihuan@kylinos.cn> <20250606082244.GL30486@noisy.programming.kicks-ass.net> <83513599-e007-4d07-ac28-386bc5c7552d@kylinos.cn> <775aaf10-3d19-4d5a-bf2b-703211166be4@redhat.com> <7d70334a-2e0a-4d1e-b4d0-64d0e3aa5439@kylinos.cn> 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: <7d70334a-2e0a-4d1e-b4d0-64d0e3aa5439@kylinos.cn> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: Oowuq-7DI32Z3SocqrE1kpfMZXmtnSxfEW-rYIEsKHc_1750247663 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: aeye9s3j7chec4p8ikdmcbiogmbj1gbd X-Rspamd-Queue-Id: 165361C0007 X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1750247667-834836 X-HE-Meta: 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 gOF/h1jA CRCKzEzXllMrUqrVoeAEwmEhruf0kzSc2ossBTfo+s9bA7KreZ1hMrLdfKhQXrv496dPbYVTJyruZPy3dnY/9RKOKqaJl15/TE44LJSln75lFGjoQ7qrQtAQxDnakEUTRmrcc1lYYj4vsLNt9qXF1uM7kStQe/bl4Qd9J1dJpyzsRRvxJ+BuV9aorljuZ4CTM4hc34fOygvIsjA1zhvUer1SxkDLP3T88/KlgyN+rVjrqEbA4LwigIYsIJ3oZR9e3DIgC/ah4JZQ7nEVLdPfqYux2+rKBJSIDBJCO2FjV9rEUKbkzAhKlFE7h9QJ6HcHaj+HvuFtgtSG99emGSQ/fR9KyBQgSWiArShdppj1aS6oyTeiZRl4xPZ50KLppdEo+6lwN7jsUtlHEtRsIwWACwjKNbTHCVdaP4iI+g+OTiAzY/+w= 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 18.06.25 13:30, Zihuan Zhang wrote: > Hi David, > > 在 2025/6/16 15:45, David Hildenbrand 写道: >> >>>> [...] >>> In our test scenario, although new processes can indeed be created >>> during the usleep_range() intervals between freeze iterations, it’s >>> actually difficult to make the freezer fail outright. This is because >>> user processes are forcibly frozen: when they return to user space and >>> check for pending signals, they enter try_to_freeze() and transition >>> into the refrigerator. >>> >>> However, since the scheduler is fair by design, it gives both newly >>> forked tasks and yet-to-be-frozen tasks a chance to run. This >>> competition for CPU time can slightly delay the overall freeze process. >>> While this typically doesn’t lead to failure, it does cause more retries >>> than necessary, especially under CPU pressure. >> >> I think that goes back to my original comment: why are we even >> allowing fork children to run at all when we are currently freezing >> all tasks? >> >> I would imagine that try_to_freeze_tasks() should force any new >> processes (forked children) to start in the frozen state directly and >> not get scheduled in the first place. >> > Thanks again for your comments and suggestion. > > We understand the motivation behind your idea: ideally, newly forked > tasks during freezing should either be immediately frozen or prevented > from running at all, to avoid unnecessary retries and delays. That makes > perfect sense. > > However, implementing this seems non-trivial under the current freezer > model, as it relies on voluntary transitions and lacks a mechanism to > block forked children from being scheduled. > > Any insights or pointers would be greatly appreciated. I'm afraid I can't provide too much guidance on scheduler logic. Apparently we have this freezer_active global that forces existing frozen pages to enter the freezing_slow_path(). There, we perform multiple checks, including "pm_freezing && !(p->flags & PF_KTHREAD)". I would have thought that we would want to make fork()/clone() children while freezing also result in freezing_slow_path()==true, and stop them from getting scheduled in the first place. Again, no scheduler expert, but that's something I would look into. -- Cheers, David / dhildenb