From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 786D428CF42 for ; Thu, 9 Oct 2025 09:19:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760001553; cv=none; b=nvOj3xl/xIlOwxmSXhsoGkVMFxjuLB0P4gixNYTgkZ+qBBmuGa/WBX0wYqU3ge0QrwG7Ji4qOzhxvwS00CUSv2SNhZIeG9a5isk0tDzvnEErTB6UzYyNDmyIkgzIiv5dyDQWHOwrGITwQUGz1bPCBIcMYfeex4VT6jPYSeANrEo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760001553; c=relaxed/simple; bh=iAbbBMOs6KgHnQbdcFFLs+hJKFOpiHY/OWCzq6L2+2k=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=BjbRhVwOquao/XFJObeO0rdxcMenaH9aZbOB9Ed7dYLCp3qyJkOqlPq8BFQYPPCbRo7ldgLhfleFevOFV0MRmruXvo2N9N8mjbF7vSVld8ngnG+i4d0VJzvsMdr4dyqe4JdSkwRrIRJuVHB/rwLmDaEXrJuAeMMKTHXtc6Mma80= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=ilgZSr2H; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="ilgZSr2H" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1760001550; 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=ym+DdkcmRG4wvpfz5ykb6s+kf1elRde6oG+aT4Hjw8w=; b=ilgZSr2HEImNC5QZj95O0lu8TUGYqTX2fQ6e6IlYDAP1wnBuq5sexMcb++pbEsDwx/yn6r TEmETUzcno/2kF9RJGMv1JF5v4TjGqV9iQgTvKmqJ2n7FuUHrCrezjvXLyz0L2FWtHWUJX qBdt5xgxV4EXb7NNfVK+cmyi5VyCIek= Received: from mail-wm1-f69.google.com (mail-wm1-f69.google.com [209.85.128.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-519-23orbOXZNAWo8CcNZ7sCYw-1; Thu, 09 Oct 2025 05:19:08 -0400 X-MC-Unique: 23orbOXZNAWo8CcNZ7sCYw-1 X-Mimecast-MFC-AGG-ID: 23orbOXZNAWo8CcNZ7sCYw_1760001547 Received: by mail-wm1-f69.google.com with SMTP id 5b1f17b1804b1-46e38957979so3306705e9.3 for ; Thu, 09 Oct 2025 02:19:08 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1760001547; x=1760606347; h=content-transfer-encoding:in-reply-to: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=ym+DdkcmRG4wvpfz5ykb6s+kf1elRde6oG+aT4Hjw8w=; b=fOKq9V9esjM8TSC3IVaRbF7/PPC5DSCmxcSvo9fh0ndngq82QTBgcLwyxhiISSOge8 1rYpnoHoxcy+exe0FE3gC+k77W7B6DYjKb3Lexc91tK7wlFCU0f/af7LCY98tHYt1rzF lg9SqU1zEpnDkZ/YO8H3JM6UUCbHuA791WW/Un9Xr6FG+ASYY68IsyTTkXd7EGfGqBSX 25tCT3sXVYxwsVxF6a3CVLZysSs6zYDvdwHu1qTv39K52h2C264XQ3jouCdDmec+f+QQ 7/y38qsgK5jewRiYIbJpVxffHl4vUNlyEHFATnvXHA8cymtxqHRj76O6RwLkT63IDD3s eoEw== X-Forwarded-Encrypted: i=1; AJvYcCUaGsdZKLqIFPLx+fDIwzY7kc/u04T1FP+sj8giVmHGB0spTLaaH3wjBgE6usW0a4EL2BX2lOR0BnjRRDI=@vger.kernel.org X-Gm-Message-State: AOJu0Yzmf0QCEYCRHPySktbad0Z8yAhhx8TgkdqpkW9OVPuAaMx3Yaro qosYXe4S4pXiQNEYeg3bhv+R97am4WSJxbXkE7NU60ePsXM+fyLRSLDNTS9zYIaqnhfyjKBHv6u 7lojVNyrmDvIp56OUhNkIkQKPwe+oPKvuMzq/Aq/EdKUYbZ2RfpnNysIS8czAFUjaXg== X-Gm-Gg: ASbGnct7lXhZvSJ7GSPpVGPaRaQ4yLl50ZhU/02BenU7tpEBDnnD1EasxYUVTidJvH2 n1KeRIaYy+/7H5pgxURIY6KZg5SCxRib7uQkm0h4eCgZGkjMKUAG8JRiqjtTeZSo/5BW5/kgrly bnJaUl5Ayb39T2Rke2P5LAZzzEQPon/3d2G+Dz2qe+86Qg5hBiHM8Ha7y/ILogofk68MjpPl9/7 e3tQUZskWTGqeHJwq/FyWeZgF+5hcs/944H3HY3/HLwxQs0g++ZIlfuX6BSW3Y50cTUKUGmFRyA h/UBuIQEEkOwklPCtsaiJwb/Q5G31L9UjD+dSzDuwQAOsSFHddyL53skicrLR19gi0bSbCf8bU+ JJ2CPvRXj X-Received: by 2002:a05:600c:c4a3:b0:46e:1fc2:f9ac with SMTP id 5b1f17b1804b1-46fa9a98fc7mr50624125e9.10.1760001547017; Thu, 09 Oct 2025 02:19:07 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFReIJdkF3acFZPAnWeL0i3BOZQC/foYxEC2R8ZxnsgKIO/Vq2BUJi9cBf7+x2XtZK2O/u2OA== X-Received: by 2002:a05:600c:c4a3:b0:46e:1fc2:f9ac with SMTP id 5b1f17b1804b1-46fa9a98fc7mr50623665e9.10.1760001546471; Thu, 09 Oct 2025 02:19:06 -0700 (PDT) Received: from [192.168.3.141] (tmo-083-189.customers.d1-online.com. [80.187.83.189]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4255d8a6daasm34080730f8f.7.2025.10.09.02.19.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 09 Oct 2025 02:19:05 -0700 (PDT) Message-ID: <129379f6-18c7-4d10-8241-8c6c5596d6d5@redhat.com> Date: Thu, 9 Oct 2025 11:19:02 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 mm-new 03/11] mm: thp: add support for BPF based THP order selection To: Yafang Shao Cc: Zi Yan , Alexei Starovoitov , Johannes Weiner , Andrew Morton , baolin.wang@linux.alibaba.com, Lorenzo Stoakes , Liam Howlett , npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, usamaarif642@gmail.com, gutierrez.asier@huawei-partners.com, Matthew Wilcox , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Amery Hung , David Rientjes , Jonathan Corbet , 21cnbao@gmail.com, Shakeel Butt , Tejun Heo , lance.yang@linux.dev, Randy Dunlap , bpf , linux-mm , "open list:DOCUMENTATION" , LKML References: <20250930055826.9810-1-laoar.shao@gmail.com> <20250930055826.9810-4-laoar.shao@gmail.com> <27e002e3-b39f-40f9-b095-52da0fbd0fc7@redhat.com> <7723a2c7-3750-44f7-9eb5-4ef64b64fbb8@redhat.com> <96AE1C18-3833-4EB8-9145-202517331DF5@nvidia.com> From: David Hildenbrand Content-Language: en-US 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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 08.10.25 15:11, Yafang Shao wrote: > On Wed, Oct 8, 2025 at 8:07 PM David Hildenbrand wrote: >> >> On 08.10.25 13:27, Zi Yan wrote: >>> On 8 Oct 2025, at 5:04, Yafang Shao wrote: >>> >>>> On Wed, Oct 8, 2025 at 4:28 PM David Hildenbrand wrote: >>>>> >>>>> On 08.10.25 10:18, Yafang Shao wrote: >>>>>> On Wed, Oct 8, 2025 at 4:08 PM David Hildenbrand wrote: >>>>>>> >>>>>>> On 03.10.25 04:18, Alexei Starovoitov wrote: >>>>>>>> On Mon, Sep 29, 2025 at 10:59 PM Yafang Shao wrote: >>>>>>>>> >>>>>>>>> +unsigned long bpf_hook_thp_get_orders(struct vm_area_struct *vma, >>>>>>>>> + enum tva_type type, >>>>>>>>> + unsigned long orders) >>>>>>>>> +{ >>>>>>>>> + thp_order_fn_t *bpf_hook_thp_get_order; >>>>>>>>> + int bpf_order; >>>>>>>>> + >>>>>>>>> + /* No BPF program is attached */ >>>>>>>>> + if (!test_bit(TRANSPARENT_HUGEPAGE_BPF_ATTACHED, >>>>>>>>> + &transparent_hugepage_flags)) >>>>>>>>> + return orders; >>>>>>>>> + >>>>>>>>> + rcu_read_lock(); >>>>>>>>> + bpf_hook_thp_get_order = rcu_dereference(bpf_thp.thp_get_order); >>>>>>>>> + if (WARN_ON_ONCE(!bpf_hook_thp_get_order)) >>>>>>>>> + goto out; >>>>>>>>> + >>>>>>>>> + bpf_order = bpf_hook_thp_get_order(vma, type, orders); >>>>>>>>> + orders &= BIT(bpf_order); >>>>>>>>> + >>>>>>>>> +out: >>>>>>>>> + rcu_read_unlock(); >>>>>>>>> + return orders; >>>>>>>>> +} >>>>>>>> >>>>>>>> I thought I explained it earlier. >>>>>>>> Nack to a single global prog approach. >>>>>>> >>>>>>> I agree. We should have the option to either specify a policy globally, >>>>>>> or more refined for cgroups/processes. >>>>>>> >>>>>>> It's an interesting question if a program would ever want to ship its >>>>>>> own policy: I can see use cases for that. >>>>>>> >>>>>>> So I agree that we should make it more flexible right from the start. >>>>>> >>>>>> To achieve per-process granularity, the struct-ops must be embedded >>>>>> within the mm_struct as follows: >>>>>> >>>>>> +#ifdef CONFIG_BPF_MM >>>>>> +struct bpf_mm_ops { >>>>>> +#ifdef CONFIG_BPF_THP >>>>>> + struct bpf_thp_ops bpf_thp; >>>>>> +#endif >>>>>> +}; >>>>>> +#endif >>>>>> + >>>>>> /* >>>>>> * Opaque type representing current mm_struct flag state. Must be accessed via >>>>>> * mm_flags_xxx() helper functions. >>>>>> @@ -1268,6 +1281,10 @@ struct mm_struct { >>>>>> #ifdef CONFIG_MM_ID >>>>>> mm_id_t mm_id; >>>>>> #endif /* CONFIG_MM_ID */ >>>>>> + >>>>>> +#ifdef CONFIG_BPF_MM >>>>>> + struct bpf_mm_ops bpf_mm; >>>>>> +#endif >>>>>> } __randomize_layout; >>>>>> >>>>>> We should be aware that this will involve extensive changes in mm/. >>>>> >>>>> That's what we do on linux-mm :) >>>>> >>>>> It would be great to use Alexei's feedback/experience to come up with >>>>> something that is flexible for various use cases. >>>> >>>> I'm still not entirely convinced that allowing individual processes or >>>> cgroups to run independent progs is a valid use case. However, since >>>> we have a consensus that this is the right direction, I will proceed >>>> with this approach. >>>> >>>>> >>>>> So I think this is likely the right direction. >>>>> >>>>> It would be great to evaluate which scenarios we could unlock with this >>>>> (global vs. per-process vs. per-cgroup) approach, and how >>>>> extensive/involved the changes will be. >>>> >>>> 1. Global Approach >>>> - Pros: >>>> Simple; >>>> Can manage different THP policies for different cgroups or processes. >>>> - Cons: >>>> Does not allow individual processes to run their own BPF programs. >>>> >>>> 2. Per-Process Approach >>>> - Pros: >>>> Enables each process to run its own BPF program. >>>> - Cons: >>>> Introduces significant complexity, as it requires handling the >>>> BPF program's lifecycle (creation, destruction, inheritance) within >>>> every mm_struct. >>>> >>>> 3. Per-Cgroup Approach >>>> - Pros: >>>> Allows individual cgroups to run their own BPF programs. >>>> Less complex than the per-process model, as it can leverage the >>>> existing cgroup operations structure. >>>> - Cons: >>>> Creates a dependency on the cgroup subsystem. >>>> might not be easy to control at the per-process level. >>> >>> Another issue is that how and who to deal with hierarchical cgroup, where one >>> cgroup is a parent of another. Should bpf program to do that or mm code >>> to do that? I remember hierarchical cgroup is the main reason THP control >>> at cgroup level is rejected. If we do per-cgroup bpf control, wouldn't we >>> get the same rejection from cgroup folks? >> >> Valid point. >> >> I do wonder if that problem was already encountered elsewhere with bpf >> and if there is already a solution. > > Our standard is to run only one instance of a BPF program type > system-wide to avoid conflicts. For example, we can't have both > systemd and a container runtime running bpf-thp simultaneously. Right, it's a good question how to combine policies, or "who wins". > > Perhaps Alexei can enlighten us, though we'd need to read between his > characteristically brief lines. ;-) There might be some insights to be had in the bpf OOM discussion at https://lkml.kernel.org/r/CAEf4BzafXv-PstSAP6krers=S74ri1+zTB4Y2oT6f+33yznqsA@mail.gmail.com I didn't completely read through that, but that discussion also seems to be about interaction between cgroups and bpd programs. -- Cheers David / dhildenb