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Wed, 16 Dec 2020 18:31:10 +0000 Subject: Re: [PATCH v2 bpf-next 0/4] introduce bpf_iter for task_vma To: Song Liu CC: bpf , "netdev@vger.kernel.org" , "ast@kernel.org" , "daniel@iogearbox.net" , "andrii@kernel.org" , "john.fastabend@gmail.com" , "kpsingh@chromium.org" , Kernel Team References: <20201215233702.3301881-1-songliubraving@fb.com> <7032f6a9-ec51-51b0-8981-bdfda1aad5b6@fb.com> <192C599B-7ED6-47A5-BF83-FA25655EAE88@fb.com> From: Yonghong Song Message-ID: <5c68adc8-6af6-718a-f75a-bcc46f63c086@fb.com> Date: Wed, 16 Dec 2020 10:31:07 -0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.5.1 In-Reply-To: <192C599B-7ED6-47A5-BF83-FA25655EAE88@fb.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [2620:10d:c090:400::5:4fea] X-ClientProxiedBy: MWHPR1601CA0004.namprd16.prod.outlook.com (2603:10b6:300:da::14) To BYAPR15MB4088.namprd15.prod.outlook.com (2603:10b6:a02:c3::18) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [IPv6:2620:10d:c085:21cf::12e6] (2620:10d:c090:400::5:4fea) by MWHPR1601CA0004.namprd16.prod.outlook.com (2603:10b6:300:da::14) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3654.12 via Frontend Transport; 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Patch 4/4 adds >> >> I did not see an example for /proc/pid/smaps. It would be good if you can cover smaps as well since it is used by a lot of people. > > smaps is tricky, as it contains a lot of information, and some of these information > require architecture and configuration specific logic, e.g., page table structure. > To really mimic smaps, we will probably need a helper for smap_gather_stats(). > However, I don't think that's really necessary. I think task_vma iterator is most > useful in gathering information that are not presented in smaps. For example, if a > vma covers mixed 2MB pages and 4kB pages, smaps won't show which address ranges are > backed by 2MB pages. Let us remove "/proc/pid/smaps" from cover letter description then. Could you add the above information to the patch #1 (and possibly cover letter as well) of the series? This can serve one of reasons why we introduce task_vma iter. Maybe you want to extend bpf programs to cover this use case. > > I have a test BPF program that parses 4-level x86 page table for huge pages. Since > we need bounded-loop to parse the page table, the program won't work well for too > big vma. We can probably add this program to samples/bpf/, but I think it is not > a good fit for selftests. This can be done later. > > Thanks, > Song >