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 49D1FEB597E for ; Wed, 11 Feb 2026 09:05:10 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 3E5DE6B0005; Wed, 11 Feb 2026 04:05:09 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 393626B0089; Wed, 11 Feb 2026 04:05:09 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 268696B008A; Wed, 11 Feb 2026 04:05:09 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 12BEB6B0005 for ; Wed, 11 Feb 2026 04:05:09 -0500 (EST) Received: from smtpin02.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id A88121402F8 for ; Wed, 11 Feb 2026 09:05:08 +0000 (UTC) X-FDA: 84431591496.02.9360646 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf09.hostedemail.com (Postfix) with ESMTP id DFBC2140002 for ; Wed, 11 Feb 2026 09:05:06 +0000 (UTC) Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=HendglcX; spf=pass (imf09.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=1770800706; 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=h+ON3hPP5/P3jT1LxaRTP3uhuvBn0Mjfpx2JhpRXZCc=; b=oVfH/ZRi3pSg9tXOTGTQtgoc8bso1dp4sBBncgnuMMNTfm1QyDcjUJtJiEpWyyLSX1mnVM dw+tKi0pOqLOBiHEEVyzA1XwmLOCBx2/t7MjnjRlJK7uXP0wLNzMBuzmGPz0O8jTOJ0Cbx Ut1kBMd61eySxxfUQ0DWsr2rz9VonTU= ARC-Authentication-Results: i=1; imf09.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=HendglcX; spf=pass (imf09.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=1770800706; a=rsa-sha256; cv=none; b=H1A6cyN73bdCJYVbC2U79CDlU7PIqTmS+YrJJWHTDL/1NkNIXqsB0NB9Fh6JtFmw74+LGV 9cs7WnQruSUdK0gj8nLdpKvWOlWp7mUmblZQ+rDJvXimhke9kATwe50k6xwO++CB1eDfy1 C3uWtodynQkrbIJQReqsSAsYHPuOL8E= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 296B660130; Wed, 11 Feb 2026 09:05:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 65AECC4CEF7; Wed, 11 Feb 2026 09:05:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770800705; bh=hWUvEIMDgaSkuvkIhEUyb9sETUNymoRMqbQf8BchU9k=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=HendglcX9VxNmWhUJdQ0Ro7+mrzywKoXELy0fHe4P1o9Vl0ijmm7Xnd906z5j6SMP zb1/B1Cmq1HLEPLxBWbl+UWMyat+ixZhN9/pxNbI4HonAcT0foY/PUvEP37zu+4wq6 AhBSRQo1Dw9qzA7A7DEM14dsAGdQkbK0HkCmF9/GSMnF+1N9IGarXcAgUStXYETF2Z 9Nd5CSFKveZJgW+jNw0qt+oej/ToUfO3CDT+wq83MawG0W53yiCO41kqLu5mkJbev3 oRxqtTbSt3ubX2ia1crF52NO981fIWmkkRoh6gHJ12GGIEHTdqNcov03GEwgMkxpyh bGB9zIIYo87MQ== Message-ID: <201fcbb4-c43c-406c-ad54-f2c9301c12b0@kernel.org> Date: Wed, 11 Feb 2026 10:05:00 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] mm: only set fault addrsss' access bit in do_anonymous_page To: Wenchao Hao Cc: Andrew Morton , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260210043456.2137482-1-haowenchao22@gmail.com> <5c4d773c-e3e7-4a71-b250-91701cbdd4a2@kernel.org> 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-Rspamd-Server: rspam12 X-Stat-Signature: 67wx4numnaxz6nnhy9p44ncrdtcd3k6f X-Rspamd-Queue-Id: DFBC2140002 X-Rspam-User: X-HE-Tag: 1770800706-712788 X-HE-Meta: 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 wQUiO2Pu NBHxaiUs3+7sx2PuIujCYDRstTZoTx8j7QxOm2vvqEae/zh9shDr9iAf74UN9i+Yt9rzIzOt0R1+kjSznLnWi2sfLbgCUQUsGZdWOkLLyxbQ7jdwZiXitG6TzwQ9Ev+m2SUd0j1zj3B5dDv+GXnKW6sJb25zgfS5lvR8efZCM4ALGW+ifeW8xzYwgF48TPDCVcdyr6TGywdbk0h1Wk0wWk2SH8CaYTjwaFFZDzjy5w/GeZsefU18hHWLID6QveCmbiE4W7la/OgNc9jal45+qrEGccxgqJA0mc9AwZXlyAXvcX0D6eOFEeyrcsmSQ5IReewzjWshjbXOSX5eKoMZXNy3999ePsyY9bSqi 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 2/11/26 01:49, Wenchao Hao wrote: > On Tue, Feb 10, 2026 at 5:07 PM David Hildenbrand (Arm) > wrote: >> >> On 2/10/26 05:34, Wenchao Hao wrote: >>> When do_anonymous_page() creates mappings for huge pages, it currently sets >>> the access bit for all mapped PTEs (Page Table Entries) by default. >>> >>> This causes an issue where the Referenced field in /proc/pid/smaps cannot >>> distinguish whether a page was actually accessed. >> >> What is the use case that cares about that? >> > > We have enabled 64KB large folios on Android devices, which may introduce > some memory waste. I want to figure out the proportion of memory waste > caused by large folios. Reading the "Referenced" field from /proc/pid/smaps > is a relatively low-cost method. Right. And that imprecision is to be expected when you opt-in into something that manages memory in other granularity and only has a single a/d bit: a large folio. Sure, individual PTEs *might* have independent a/d bits, but the underlying thing (folio) has only a single one. And optimizations that build on top (pte coalescing) reuse that principle that having a single logical a/d bit is fine. > > Additionally, considering future hot/cold page identification, we aim to > detect 64KB large folios where some pages are actually unaccessed and split > them into normal pages to avoid memory waste. > > However, the current large folio implementation sets the access bit for all > page table entries (PTEs) of the large folio in the do_anonymous_page > function, making it hard to distinguish whether pre-allocated pages were > truly accessed. The deferred shrinker uses a much simpler mechanism: if the page content is zero, likely it was over-allocated and never used later. It's not completely lightweight (scan pages for 0 content), but is reliable, independent of the mapping type (PMD, cont-pte, whatever) and independent of any access/dirty bits, leaving performance unharmed. When you say "I want to figure out the proportion of memory waste", are we talking about a debug feature? -- Cheers, David