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 37DDDE9A03E for ; Tue, 17 Feb 2026 20:29:12 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 6874A6B00A3; Tue, 17 Feb 2026 15:29:11 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 635396B00A4; Tue, 17 Feb 2026 15:29:11 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 509BF6B00A5; Tue, 17 Feb 2026 15:29:11 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 3A4906B00A3 for ; Tue, 17 Feb 2026 15:29:11 -0500 (EST) Received: from smtpin02.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id CAF8F1C0EE for ; Tue, 17 Feb 2026 20:29:10 +0000 (UTC) X-FDA: 84455088060.02.3186160 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf26.hostedemail.com (Postfix) with ESMTP id 207F614000C for ; Tue, 17 Feb 2026 20:29:09 +0000 (UTC) Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=DzqZia3n; spf=pass (imf26.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=1771360149; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to: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=7WCESJSbY9N2dO2UAxDeDl2USAxOA6BbU696flxTd7A=; b=wgnFO85mFH7GnnpYN32BwteNx/SCNJlCTqgRBr2BdwKiHzo6WyT8AKWdlaZORjCdnmGb1A uqu2RHdotkrmS9acCPeRBg2M4BCz7a6NRiaz6/oLVzUNgkB04WXpAvkGW59JuvWcaI4RLv dpe+jRE374YR/mvFxp7n8ZfJj/+8uK0= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=DzqZia3n; spf=pass (imf26.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-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1771360149; a=rsa-sha256; cv=none; b=u7vhShylX17mudyE47Z7qdIUPtAMu1FfdmPJnROb8xVzkUThTE+WooOyWgB4UgKRdZBttg j0ibr7DEBpWgv2OOK7Mh9nVVMDaDw+XFN4QqqmrQ59slifU21gh+bH4Yrl1QAoP90HKo3F KsgaahFXRNIPlcVdf7Qdqxew7bX1YhI= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 7A1CB60053; Tue, 17 Feb 2026 20:29:08 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 63F1DC19425; Tue, 17 Feb 2026 20:29:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771360148; bh=galDsGJIDowpQEwDMBvPkSWhLfNMwM+9UqHQmmxkw6U=; h=Date:Subject:To:References:From:In-Reply-To:From; b=DzqZia3nlIi0O0fad+QBa4AqAo8vQWRTVvnHJhdS3cosLARHKY6/9a9UtBr+MDbLL 1fjob+YIkLg411pUQEci64PNmZfAdMb1+GMtbsnE92FuNZDR77xwNMy1s+blKy6Z2o fHO6H5xdYn81X5vQK8Y5YKWEVzLJW3l+G20geIA1rDg6V1NrVglwUa0EEa8HkDP064 IqoQ6sUD+bYDAkf3Twf3G88S18HSOESBgB5R3fWLG7bgIHXn+iNs1Cxd1JMBATRvvf P7HrdY4VBkZxZbJI9r9yI5o0JaZ4bd0Wxz4oRRW8ddITv/CtDiPpT9P9WNHrJK4P2f l8+1lX+D/q6mA== Message-ID: <419053a2-9784-4051-b73e-5871d3c32be9@kernel.org> Date: Tue, 17 Feb 2026 21:29:02 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: Add AnonZero accounting for zero-filled anonymous pages To: Wenchao Hao , Andrew Morton , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Kiryl Shutsemau References: <20260214084514.2842745-1-haowenchao22@gmail.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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 207F614000C X-Stat-Signature: f35mk9h35bzizbatbfijd7wknt1jppb9 X-HE-Tag: 1771360148-480338 X-HE-Meta: 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 721J+tNp VO31xDFV44bD+mmneFVaMB9KrLr0zdCRl0zMAOJxYlgA0HOEsGxlPpJ2vJQpVEAZ77MBR8Zc+xX40x4kg61YiokkcaJ+vThWxAMqczww1z4uh34wGa6KsORRjMwbOzpzGNpjdXOnduHlR5LWvC73hsm+sudRyD+ZcPVhgRDM6x0j85tfakqhamSuHJAADKfnmLy93rBEDsL1Di0JepMN8ug2Xoq71UOvB15agDp25c5tSAA5QuWHf/nvTyvILxOBwT5C2CkgKld+pdh+mRRxKj0EQ2pbaJoxApVhI8zM8o+Cc8w6Kn2ruALTARBM9YZ9BuUOkjGGrPdh4yKI= 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 2/17/26 16:22, Wenchao Hao wrote: > On Sat, Feb 14, 2026 at 4:45 PM Wenchao Hao wrote: >> >> Add kernel command line option "count_zero_page" to track anonymous pages >> have been allocated and mapped to userspace but zero-filled. >> >> This feature is mainly used to debug large folio mechanism, which >> pre-allocates and map more pages than actually needed, leading to memory >> waste from unaccessed pages. >> >> Export the result in /proc/pid/smaps as "AnonZero" field. >> >> Link: https://lore.kernel.org/linux-mm/20260210043456.2137482-1-haowenchao22@gmail.com/ > > Sorry for the late reply. We are now on Chinese New Year holiday, so... > > The original goal of this patch is to measure memory waste from anonymous > THPs - pages pre-allocated on fault but never accessed. > > On memory-sensitive devices like mobile phones, this helps us make better > decisions about when and how to enable THP. I think this is useful for > guiding THP policies, even as a debugging feature. > > Let me summarize the discussion so far: > - Matthew Wilcox questioned the value and raised concerns fork but haven't > exec path > - Michal Hocko criticized the inefficiency of scanning zero-filled pages. > - Kiryl Shutsemau prefers a system-call-based interface. > - David Hildenbrand acknowledged the value and suggested implementation > improvements. > Please correct me if I missed or misrepresented anything. > > I suggest we first agree whether this functionality is useful for upstream, > before discussing implementation details. > > Reasons why this should go upstream from me: > > - Anonymous THP can introduce real memory waste, but we currently have no > good way to measure it. > - With accurate metrics, we can make better THP policy: disable for > low-utilization cases, or early-unmap to relieve memory pressure and so > on. This is especially valuable for mobile/embedded devices. > > Possible implementations: > > 1. A new smaps counter (default-off) to count zero-filled pages. > 2. A new madvise command like MADV_GET_ZEROPAGE > 3. A dedicated system call I understand Kiyls point about smaps providing too much information users might not be interested in already. So sorting that out might provide a real benefit to other users that are only interested in specific stats (e.g., Rss). Providing a system call where one can specify/filter in theory sounds like a good idea. A syscall implies that one has to write a tool to obtain these metrics. The nice thing about smaps/smaps_rollup is that it can be easily consumed on any system while debugging. I wonder if there could be a way to achieve something similar with a file. Likely not, but maybe someone reading along can surprise me :) Otherwise we'd have to go with a tool. -- Cheers, David