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]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D93E7C5DF66 for ; Mon, 17 Aug 2026 18:10:39 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id D0EA86B011B; Mon, 17 Aug 2026 14:10:38 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id CEC5F6B02DE; Mon, 17 Aug 2026 14:10:38 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id BFC7A6B0468; Mon, 17 Aug 2026 14:10:38 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 915A16B011B for ; Mon, 17 Aug 2026 14:10:38 -0400 (EDT) Received: from smtpin21.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id DBE12408BC for ; Mon, 17 Aug 2026 18:10:34 +0000 (UTC) X-FDA: 85111551588.21.E7EC7B0 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf20.hostedemail.com (Postfix) with ESMTP id 2D8331C0002 for ; Mon, 17 Aug 2026 18:10:32 +0000 (UTC) Authentication-Results: imf20.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=P6u3cyJO; spf=pass (imf20.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1786990233; 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=IWschY6PJIJj78TPAK68wuF6XfNqvRhD4s+H+yde0ec=; b=up1tuZCi529sHGSVaV1K86bid/1yyI+U2BGmCgd1jkpE4vAoDGLvD3D7SwSA8ycWRBqpxH Cj6WwpQ3N4dWPjTOQZr5cJWc4VTUBjnLCSsfhBfKYjIHMs3u3nAHS2HiBYSY2d3UM+m6iV xzyfbBbQtdcqY/Yus4YmJClirxCw86U= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1786990233; b=4YCb3dJPArrVIHbIq7Gq9PzHlwMrWhJaw87gnngokqBKkYt3l9ZLBu58QeIR+C0GPdBAr8 fiZ8FvHgGZmemv8kExvDTG7QCSDjUsTcXcZDnlFtXo7wk52pe506DWr373F/ymkcQHul9h Fa51OOQuOkh8VsA7Es1prcoqh9BsT7w= ARC-Authentication-Results: i=1; imf20.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=P6u3cyJO; spf=pass (imf20.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 9A90F600AE; Mon, 17 Aug 2026 18:10:32 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7283B1F000E9; Mon, 17 Aug 2026 18:10:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786990232; bh=IWschY6PJIJj78TPAK68wuF6XfNqvRhD4s+H+yde0ec=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=P6u3cyJOWqTGgmW2GpD2BfOMO+B6rcLUTroOW0CnhXHdzCA9hhbVgBoQyJnIMYQln ixmfd+ipl+0hMRrTCQiawq5EZ4qv193Fdt/sAatEejaoei9OExsjZVIXOVxID4VkuY KquJ+6JlpsFLMatZHvmkhsSVsjCPOWirDHXQ31UPChw/MI7AzicEq10JTfjGVF04Xc eqVWKErNMzostAW2c98rp/7g0HtznoiY7HfuAfJBD9Z7XFVhpzJCd4CdOApzkFxM95 KhB1y5lCFli53BwAp9WLWlIcxVmmW4Lg5cFVsqHGeuIDQo0/SqGXb7C4eCfabHvMS5 r/7/IUcLjvNjw== Message-ID: <04f3ce2f-67f5-4829-9551-a69b9df29854@kernel.org> Date: Mon, 17 Aug 2026 20:10:26 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC] bpf: account ring buffer backing pages separately from Lost RAM To: Xiang Gao , Andrii Nakryiko Cc: Alexei Starovoitov , Daniel Borkmann , Andrew Morton , yinchuang1@xiaomi.com, bpf@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Xiang Gao , "Lorenzo Stoakes (Arm)" , Steven Rostedt References: <20260815091819.3651099-1-gaoxiang17@xiaomi.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+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: <20260815091819.3651099-1-gaoxiang17@xiaomi.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: i688ir1taecqsjsdj9f4eujajzgoq5op X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 2D8331C0002 X-HE-Tag: 1786990232-344412 X-HE-Meta: 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 eviVfJiw 9kYRoIs7i+ZYEYm5Nb5Ee63Ej9wu/9JOvoqL7Xt8on5rxp88ISFZhj5UMKt65oPaFIyqMAGVyEdW9/Y0cFKaeq8MrDe2feC1B6PiMlJCVW7cXb13h5soFDtn67UuFRqL8/SWF+JJkDWT0utVKupuctB7tXBk+Ts0BsiwJP21ALfWmYw1zwPaZ37+/EKgU5ltjZr/Jm4OWWoWLUx+giuIfolIhydMQkp1odWpW65XFSdHHhf9iNiBX0TcPCkDHVA9HlyvmNeX/54q/KP8OnF+8R4+JZrySBM7SJ6XAgauTnr727kwZ70/pwP6GfA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/15/26 11:18, Xiang Gao wrote: > Hi, Hi, > > I would like to discuss accounting BPF ring buffer backing pages in > system-wide memory reports. > > BPF ring buffers allocate their data and metadata as order-0 pages directly > from the buddy allocator, and then map those pages with vmap(). I assume there is a reason the slab isn't used, right? Are these pages mapped into user space such that page->mapcount would get used? Can you point me at relevant code? > > Because vmap() maps caller-owned pages, these backing pages are not counted > by VmallocUsed. They are also not slab pages. As a result, most BPF ring > buffer memory is not represented by an existing named /proc/meminfo category > and appears as Lost RAM in Android memory reports. > > We measured this on an Android 6.18 kernel. > > Test case: > > 32 BPF ring buffer maps > 16 MiB data area per map > 512 MiB total data area > > Observed changes: > > Lost RAM: approximately +529 MiB > VmallocUsed: approximately +2 MiB > Slab: approximately unchanged > > After destroying all maps, the values returned close to baseline. > > The question is whether the kernel should expose the unique physical backing > pages of live BPF ring buffers through a dedicated global counter and a > /proc/meminfo entry, for example: > > BpfRingbuf: This looks a bit too specific for my taste. And I think we should try to no inflate these statistics here too much. > > The proposed counter would include: > > * ring buffer data pages; > * metadata pages; > * consumer and producer position pages. > > It would exclude: > > * the second virtual mapping of data pages; > * the pages[] pointer array; > * map metadata allocations; > * vmap page tables. > > The goal is to account for the currently unclassified direct backing pages. > Slab- and vmalloc-backed auxiliary allocations are already represented by > existing memory categories and should not be counted again. > > A possible implementation is an NR_BPF_RINGBUF vmstat counter maintained by > the ring buffer allocation and free paths, with the aggregate exposed through > /proc/meminfo. > > Questions: > > 1. Is a dedicated BPF ring buffer counter appropriate? I don't think so. See [1] where we just had the same discussion for tracing buffers. For them, Steve [2] had an idea on how to expose them more fine-grained and tracing specific. [1] https://lore.kernel.org/r/20260810094025.136705-1-gaoxiang17@xiaomi.com [2] https://lore.kernel.org/r/20260810105710.6ee5e493@gandalf.local.home > 2. Should this be represented as an NR_* vmstat counter? I don't think so. > 3. Is /proc/meminfo an acceptable interface for this information? Again, I don't think so. "Lost RAM" really is just "excessive memory allocated by some other subsystem". I agree that some users might want to figure out what is consuming that much memory, but I don't think growing /proc/meminfo in that way is really what we want. > 4. Is counting only unique physical backing pages the correct accounting unit? I'd assume the "It would exclude" part above should not be accounted there, if that's what you mean. -- Cheers, David