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 C5D4EC54ED1 for ; Tue, 27 May 2025 09:27:46 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 5A0FB6B0093; Tue, 27 May 2025 05:27:46 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 52AB06B0098; Tue, 27 May 2025 05:27:46 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3CBB66B0099; Tue, 27 May 2025 05:27:46 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 19D5C6B0093 for ; Tue, 27 May 2025 05:27:46 -0400 (EDT) Received: from smtpin30.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 642DF1404D5 for ; Tue, 27 May 2025 09:27:45 +0000 (UTC) X-FDA: 83488160490.30.705FEDD Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf30.hostedemail.com (Postfix) with ESMTP id CC3F28000B for ; Tue, 27 May 2025 09:27:42 +0000 (UTC) Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=OG4CQPF4; dmarc=pass (policy=quarantine) header.from=redhat.com; spf=pass (imf30.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 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=1748338063; 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=YYhQpMO1cqk6PzoLJg9BrpHx0v/xNedZXm7uLXOi+48=; b=yybee/hO7DcOY+VuVJ/0Tx4L+WbDV1ZpJGwRTu2rLjThgkTva7nFbuHQcu+5tlGdd8OUxo xwpFKY8qpPcMKQmpU5kqc4JPWfFBQYSn4uWBRdC20pmjx20tL905ccpqdNaakvvlL5uEIp 0xpwXEY7IpB0exo3h9UwGD+QyrfyLgk= ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=OG4CQPF4; dmarc=pass (policy=quarantine) header.from=redhat.com; spf=pass (imf30.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1748338063; a=rsa-sha256; cv=none; b=w4Wuhu+vyN6Eu6zlFV8GSxgsj/phlr6pcFXXrpTd5wkAZb/mezpanXR8gYu/KYxRT2YZaX JH0U5MQDIJXcAMJ/1XlmFfe1laJbjp6ClFUvZyTSWClESuBFKeijl6LN7g2XnhbZzEg3yt 97XkLAaDpftOx3dlo1+lsqBLwJTZIlg= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1748338062; 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=YYhQpMO1cqk6PzoLJg9BrpHx0v/xNedZXm7uLXOi+48=; b=OG4CQPF4I4K58/EYQk2TJEQX3Fc71LYNL8AHG8B7SjLE8tVXS1iGnvzY8YVEdsH+weBNeT OQmI7/gcC1QceYJDeG1xHFx+o0Tfv4V0eBN6Kdb9LdxyusnL+2TBIaTfvyVYNkNTOSplX0 k03Jq52TJ81yxfDM7Ke3a0BZ0F8NrMc= Received: from mail-wm1-f72.google.com (mail-wm1-f72.google.com [209.85.128.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-649-Ud9uQ8qIPh-GswRajAVRhA-1; Tue, 27 May 2025 05:27:40 -0400 X-MC-Unique: Ud9uQ8qIPh-GswRajAVRhA-1 X-Mimecast-MFC-AGG-ID: Ud9uQ8qIPh-GswRajAVRhA_1748338059 Received: by mail-wm1-f72.google.com with SMTP id 5b1f17b1804b1-44b1f5b91c1so23780835e9.1 for ; Tue, 27 May 2025 02:27:40 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1748338059; x=1748942859; 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=YYhQpMO1cqk6PzoLJg9BrpHx0v/xNedZXm7uLXOi+48=; b=xHutrDn39iAiDw40nbobNh3kQH8uFI+pOAJEul7G2DHy3OuXm1gf8338TM26nvWqLY D+3lDkM8S5E8t8ygNz0Qec0ryw3czCN60MXPhL8zD788DS2DKwqV2Qfa7G+tXXqg81ff BW8JmRKnmFplccjtU0A0D+lkOCkP51YEOAoG6aC98muq8my3QeOuQZIii//8wzclX8RL Im+rHj/HSBDh0s3hXaRfAV08L/3TOk4KUCgf+bMcXBZYrbl9vgYcWqMtuRPvLMXiSBf3 cEvArRY96DQY+O5GyGAvE50biNr93yeOGiq8O1u5tPrGe6VsYHdNis0b16NWMi2NzDdR MqXQ== X-Forwarded-Encrypted: i=1; AJvYcCUMEsK0+4sD3jXrEUghs1yXCJ0bxThcNXHyjqSvuX68hHpy87sMaP6k1oO2kLw+gIYLzi5Q/h9FdA==@kvack.org X-Gm-Message-State: AOJu0Yx4QPPBavCsyQz6W9b9id/C0rW1p8AJC1UIUMiFLqN4qPCd9NW6 hUDN4loUaWVzMScf/Z5b8dLo1V5NMg0Y/bQtO09/klSNi2hp8ngMRmorZ0KXT0dWIjfRi0fkh+W 42E54aWQXI5h/RvPcPrv+4atWiNjWl0uDZxWHBLzyoMUmAzXpNtTX X-Gm-Gg: ASbGncsw/sXtvLHmTkBK7ibC8l9HRMBgyE1ErA+eX1LWpj2R3uxVOpuAl0qjDbgeLRI Aqso0j/fgwaDZC+cjnnzltf9q8m6NguPeQrs9ov3ggL0zXygRAMERtXFyLoHF++YUCMprGnPlXl 6aXQLJivMgED/46TQszsUS2JW8gxkECHmY/2/SLkCtLI3t9/k/llj9HvmudE4t7w3zdtIWoeLiO UJstAkWqZFkZgM3bZXQa7obIQdITa9usObidrTlGgTY7jl1miKhnqVRgNyUW7a/XkeWr1PZcI0A UaX/hhqalQShj9+ksWhuD6JCMm1iozoh1235zqt6m0xY X-Received: by 2002:a05:600c:a07:b0:43c:fdbe:4398 with SMTP id 5b1f17b1804b1-44c916071admr105759785e9.6.1748338059238; Tue, 27 May 2025 02:27:39 -0700 (PDT) X-Google-Smtp-Source: AGHT+IF1TOsrwysWdxzl529keu1uTVd98UIgX+NLVxEQsxAC8CJwO2infiezFFhayliHYN3MBxdvoA== X-Received: by 2002:a05:600c:a07:b0:43c:fdbe:4398 with SMTP id 5b1f17b1804b1-44c916071admr105759355e9.6.1748338058717; Tue, 27 May 2025 02:27:38 -0700 (PDT) Received: from ?IPV6:2a09:80c0:192:0:5dac:bf3d:c41:c3e7? ([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-447f23bfd54sm272682595e9.17.2025.05.27.02.27.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 27 May 2025 02:27:38 -0700 (PDT) Message-ID: <5d48d0c3-89a3-44da-bc1a-9a4601f146a4@redhat.com> Date: Tue, 27 May 2025 11:27:37 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v2 0/5] mm, bpf: BPF based THP adjustment To: Yafang Shao Cc: akpm@linux-foundation.org, ziy@nvidia.com, baolin.wang@linux.alibaba.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, hannes@cmpxchg.org, usamaarif642@gmail.com, gutierrez.asier@huawei-partners.com, willy@infradead.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, bpf@vger.kernel.org, linux-mm@kvack.org References: <20250520060504.20251-1-laoar.shao@gmail.com> <7d8a9a5c-e0ef-4e36-9e1d-1ef8e853aed4@redhat.com> <5f0aadb1-28a8-4be0-bad9-16b738840e57@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: _QjQcNT6r4bfm6Le-a5KGV4FIYOIBatmQYrv_8TjAuI_1748338059 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: CC3F28000B X-Stat-Signature: epzqs6wk4shmd5xg4xtiwhmjd4wz979g X-Rspam-User: X-HE-Tag: 1748338062-440961 X-HE-Meta: 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 +CeJ2dEH 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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 27.05.25 10:40, Yafang Shao wrote: > On Tue, May 27, 2025 at 4:30 PM David Hildenbrand wrote: >> >>>> I don't think we want to add such a mechanism (new mode) where the >>>> primary configuration mechanism is through bpf. >>>> >>>> Maybe bpf could be used as an alternative, but we should look into a >>>> reasonable alternative first, like the discussed mctrl()/.../ raised in >>>> the process_madvise() series. >>>> >>>> No "bpf" mode in disguise, please :) >>> >>> This goal can be readily achieved using a BPF program. In any case, it >>> is a feasible solution. >> >> No BPF-only solution. >> >>> >>>> >>>>> We could define >>>>> the API as follows: >>>>> >>>>> struct bpf_thp_ops { >>>>> /** >>>>> * @task_thp_mode: Get the THP mode for a specific task >>>>> * >>>>> * Return: >>>>> * - TASK_THP_ALWAYS: "always" mode >>>>> * - TASK_THP_MADVISE: "madvise" mode >>>>> * - TASK_THP_NEVER: "never" mode >>>>> * Future modes can also be added. >>>>> */ >>>>> int (*task_thp_mode)(struct task_struct *p); >>>>> }; >>>>> >>>>> For observability, we could add a "THP mode" field to >>>>> /proc/[pid]/status. For example: >>>>> >>>>> $ grep "THP mode" /proc/123/status >>>>> always >>>>> $ grep "THP mode" /proc/456/status >>>>> madvise >>>>> $ grep "THP mode" /proc/789/status >>>>> never >>>>> >>>>> The THP mode for each task would be determined by the attached BPF >>>>> program based on the task's attributes. We would place the BPF hook in >>>>> appropriate kernel functions. Note that this setting wouldn't be >>>>> inherited during fork/exec - the BPF program would make the decision >>>>> dynamically for each task. >>>> >>>> What would be the mode (default) when the bpf program would not be active? >>>> >>>>> This approach also enables runtime adjustments to THP modes based on >>>>> system-wide conditions, such as memory fragmentation or other >>>>> performance overheads. The BPF program could adapt policies >>>>> dynamically, optimizing THP behavior in response to changing >>>>> workloads. >>>> >>>> I am not sure that is the proper way to handle these scenarios: I never >>>> heard that people would be adjusting the system-wide policy dynamically >>>> in that way either. >>>> >>>> Whatever we do, we have to make sure that what we add won't >>>> over-complicate things in the future. Having tooling dynamically adjust >>>> the THP policy of processes that coarsely sounds ... very wrong long-term. >>> >>> This is just an example demonstrating how BPF can be used to adjust >>> its flexibility. Notably, all these policies can be implemented >>> without modifying the kernel. >> >> See below on "policy". >> >>> >>>> >>>> > > As Liam pointed out in another thread, naming is challenging here - >>>>> "process" might not be the most accurate term for this context. >>>> >>>> No, it's not even a per-process thing. It is per MM, and a MM might be >>>> used by multiple processes ... >>> >>> I consistently use 'thread' for the latter case. >> >> You can use CLONE_VM without CLONE_THREAD ... > > If I understand correctly, this can only occur for shared THP but not > anonymous THP. For instance, if either process allocates an anonymous > THP, it would trigger the creation of a new MM. Please correct me if > I'm mistaken. What clone(CLONE_VM) will do is essentially create a new process, that shares the MM with the original process. Similar to a thread, just that the new process will show up in /proc/ as ... a new process, not as a thread under /prod/$pid/tasks of the original process. Both processes will operate on the shared MM struct as if they were ordinary threads. No Copy-on-Write involved. One example use case I've been involved in is async teardown in QEMU [1]. [1] https://kvm-forum.qemu.org/2022/ibm_async_destroy.pdf > >> >> Additionally, this >>> can be implemented per-MM without kernel code modifications. >>> With a well-designed API, users can even implement custom THP >>> policies—all without altering kernel code. >> >> You can switch between modes, that' all you can do. I wouldn't really >> call that "custom policy" as it is extremely limited. >> >> And that's exactly my point: it's basic switching between modes ... a >> reasonable policy in the future will make placement decisions and not >> just state "always/never/madvise". > > Could you please elaborate further on 'make placement decisions'? As > previously mentioned, we (including the broader community) really need > the user input to determine whether THP allocation is appropriate in a > given case. The glorious future were we make smarter decisions where to actually place THPs even in the "always" mode. E.g., just because we enable "always" for a process does not mean that we really want a THP everywhere; quite the opposite. Treat the "always"/"madvise"/"never" as a rough mode, not a future-proof policy that we would want to fine-tune dynamically ... that would be very limiting. -- Cheers, David / dhildenb