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 F27A5FB44C5 for ; Fri, 24 Apr 2026 07:33:56 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 287A66B0005; Fri, 24 Apr 2026 03:33:56 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2126B6B008C; Fri, 24 Apr 2026 03:33:56 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 08BC36B0092; Fri, 24 Apr 2026 03:33:56 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id E70536B0005 for ; Fri, 24 Apr 2026 03:33:55 -0400 (EDT) Received: from smtpin03.hostedemail.com (lb01b-stub [10.200.18.250]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 7B2E4A06CD for ; Fri, 24 Apr 2026 07:33:55 +0000 (UTC) X-FDA: 84692635230.03.6327264 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf07.hostedemail.com (Postfix) with ESMTP id CB3C740006 for ; Fri, 24 Apr 2026 07:33:53 +0000 (UTC) Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=ET2IVhVP; spf=pass (imf07.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=1777016033; 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=i3emymLQKMW5KNMhf0/v5WxkXv+ccDytIAO46/7sqmQ=; b=s3sHOFOhpEmWvKMKAPAioptBUeJqwyHrGvol4M+fmwRSprMmg9RS/wHOfCZbT0EyMVIM5F pZ7/Sh7exfdo9c+Ns/mOU0DO5PYhrbCvsdM6ls35QV4LfOiDBq1o+YcINfcPpqcfRVQJyt 7T0vHu00sjcG+uacjrMe4mVpF4gy5xE= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=ET2IVhVP; spf=pass (imf07.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=1777016033; a=rsa-sha256; cv=none; b=7a/XNlxSi4Wv1I2vdMp4Q+ot84WL+oVO6DxYRHJprUzBNcCBlAu/+c7W27gWBD4QZoEI/K 7yyqGltLakrDnelE36KCZZbTWJMRVjoGMHSbecNJhJemTY2peDyRm3c4vrjkhfSuN2xJUE K/wEIeS2JdXZc8LkeKb6yq0RgNlwukE= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 06B366001A; Fri, 24 Apr 2026 07:33:53 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4E265C19425; Fri, 24 Apr 2026 07:33:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777016032; bh=FWUCIjlRnfU0ETPJAkdUekHGrm29nbNvT4ou3u2ZJrI=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=ET2IVhVPW1Je/rflovdV0szP2Nft7DLDtK4Cjt8gOa3tlrF0PYvVAsdr0AtKcI2nw Nq+tRJktHRoOnrRgLjk5Kv3ysZ2GmBvgxsuvvvVS0TTGEE7lrAaIzb149j1fee4kf4 suHj+w2LF9Z9O8b/zefIcUsWF1YP8BPRUf94MHKp5vYpn5HZl+5iwfqHVhO9BKX13G TokYxhGt++juL6hzDh2Tme7OW4r63MYtWKGLTq0MG3pu3l2XBFHr7Tbi8btjUy7Nuu Gn8N/LHbYUCbRCqqvn8DuTdr5+LOL4DK+dRWxwDt3pTs3GTdLY10KD3DuG7COGtHP1 QTWokFnUqoNtw== Message-ID: <0fe62163-cdfd-47e4-bc88-df7a69dc5a6d@kernel.org> Date: Fri, 24 Apr 2026 09:33:45 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 4/7] mm/sparse-vmemmap: Fix DAX vmemmap accounting with optimization To: Muchun Song , Andrew Morton , Muchun Song , Oscar Salvador , Michael Ellerman , Madhavan Srinivasan Cc: Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Nicholas Piggin , Christophe Leroy , aneesh.kumar@linux.ibm.com, joao.m.martins@oracle.com, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20260424025547.3806072-1-songmuchun@bytedance.com> <20260424025547.3806072-5-songmuchun@bytedance.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: <20260424025547.3806072-5-songmuchun@bytedance.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: od4oc1muxtqk9t1sy4bdjfyq57ceicga X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: CB3C740006 X-HE-Tag: 1777016033-377460 X-HE-Meta: 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 pRiqy/Kn Ti/N2kr4YXnxH4uhhfmH7VPx60VldwgrWrX76rBzEBEF2TrPExU+hmb5QVVzbij3WSdjORWP8mK7CiXDmDOkm+Hczrj3CApuyRPbZb0PBUcCxXEV3z4fL2NJCyajlQoBvSAmZ3OI/1n0qDLhv1eHquZdkrRc6pYgCeJ2wFfux9rltpLCP24bnSe+leqoiY2vGQzoIUxuoZTOu5kmCszXNZ7sbyCH0GG8ODiXvHLwXMmQYhUVHgKFIJw/xrrE6TKByOA2LpO4RUxee5pXNFGNhmotfixqq70uFEMmr3dfKrBmhB+diLV3PrWXNHQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/24/26 04:55, Muchun Song wrote: > When vmemmap optimization is enabled for DAX, the nr_memmap_pages > counter in /proc/vmstat is incorrect. The current code always accounts > for the full, non-optimized vmemmap size, but vmemmap optimization > reduces the actual number of vmemmap pages by reusing tail pages. This > causes the system to overcount vmemmap usage, leading to inaccurate > page statistics in /proc/vmstat. > > Fix this by introducing section_vmemmap_pages(), which returns the exact > vmemmap page count for a given pfn range based on whether optimization > is in effect. > > Fixes: 15995a352474 ("mm: report per-page metadata information") > Cc: stable@vger.kernel.org > Signed-off-by: Muchun Song > Acked-by: Mike Rapoport (Microsoft) > Acked-by: Oscar Salvador > --- > mm/sparse-vmemmap.c | 31 +++++++++++++++++++++++++++---- > 1 file changed, 27 insertions(+), 4 deletions(-) > > diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c > index 3340f6d30b01..2e642c5ff3f2 100644 > --- a/mm/sparse-vmemmap.c > +++ b/mm/sparse-vmemmap.c > @@ -652,6 +652,28 @@ void offline_mem_sections(unsigned long start_pfn, unsigned long end_pfn) > } > } > > +static int __meminit section_nr_vmemmap_pages(unsigned long pfn, unsigned long nr_pages, > + struct vmem_altmap *altmap, struct dev_pagemap *pgmap) > +{ > + const unsigned int order = pgmap ? pgmap->vmemmap_shift : 0; > + const unsigned long pages_per_compound = 1UL << order; > + > + VM_WARN_ON_ONCE(!IS_ALIGNED(pfn | nr_pages, > + min(pages_per_compound, PAGES_PER_SECTION))); FWIW, I though the right thing to do here would be: VM_WARN_ON_ONCE(!IS_ALIGNED(pfn | nr_pages, pages_per_compound); VM_WARN_ON_ONCE(!IS_ALIGNED(pfn | nr_pages, PAGES_PER_SUBSECTION); I don't really see how PAGES_PER_SECTION make sense given that PAGES_PER_SUBSECTION are the smallest granularity we allow adding/removing. Also, the "min()" implies that there is a connection between both properties, but there isn't to that degree. If order == 0, then you'd only ever check alignment for ... 1, not PAGES_PER_SUBSECTION, which already looks weird. So you really want to check "max(pages_per_compound, PAGES_PER_SUBSECTION)", but just having two statements is clearer. Or am I getting something very wrong here? :) -- Cheers, David