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 BD12010F92F2 for ; Tue, 31 Mar 2026 20:05:07 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 0A9796B0092; Tue, 31 Mar 2026 16:05:07 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 082516B0095; Tue, 31 Mar 2026 16:05:07 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id ED93B6B0096; Tue, 31 Mar 2026 16:05:06 -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 DEC2F6B0092 for ; Tue, 31 Mar 2026 16:05:06 -0400 (EDT) Received: from smtpin12.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 7FC0114025C for ; Tue, 31 Mar 2026 20:05:06 +0000 (UTC) X-FDA: 84607437012.12.5F89493 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf19.hostedemail.com (Postfix) with ESMTP id B85811A0009 for ; Tue, 31 Mar 2026 20:05:04 +0000 (UTC) Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b="R94YMlP/"; spf=pass (imf19.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=1774987504; 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=PuQ8BtDl4ZQkNykwAeFNEZvgCMdSm+IXML499Mdao5Y=; b=bvBWHEod5Y39bB9UMsRStA7hrKeoJvoS2Y2f/pSrsesTW8xUoMIDWYZ4oWJntr7GsUoNFu WQbtVu1jAdPZGHkL8DdA5xo4p7STGp4MnucnWbp2ictjOHEKMrDbT+m5XvLZC8oTfxeyBI J4TJCcjN0kIOHhPX45q6aeNFr8UDzRE= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1774987504; a=rsa-sha256; cv=none; b=sfWVq6VKVhuvlbgMWwfg1xTO2qas02gnf1Y1Be280FdMhGb/sjhFxi7K6vIgGbFMNERTxd Ieh+VimYtTjuqk33801W5NS3YvdzfqTPZjpeiWDOXyLLlE5tFVaa5hmFb103SmX1f/5lDQ n/zxlE27wppfqm9qk4H9hXzqWoIPJmI= ARC-Authentication-Results: i=1; imf19.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b="R94YMlP/"; spf=pass (imf19.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 (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 330B060128; Tue, 31 Mar 2026 20:05:04 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1FF79C19423; Tue, 31 Mar 2026 20:04:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774987503; bh=p4iHbgiMDPcx1vmH5nX95S1Qm7dNTZ6vVmQCUSuJfCk=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=R94YMlP/6+sA8K43jL2LcOK5OTgIssoC/au/el4KlnCmCHy26ih5mzqXN4myxpE85 c0nMCL2+p4iodkuzTmKEQv48Sgm8snhlUqo/oKekYWquLKA3cK+buVi5nGOzyIU3gL mfbubDsCzeKAdhVcvv0jp5+nU5NyQC2YiI22hImCYgNTwClbKEeyQ5dTondOvsaG7H PDawVk9eZVFpcw9TyG6r7nRnv5Jv3es69FrI7rsJ8Y6ktX3JBixIzkwQ+rQPjHeLHt w3/pdSuvQjhwHF10Sql5sFUw/JBIploDMSGoMp5ClfPfmffK1N1T6ZjQFkZd2IRDg7 DmS4U6pFsw0xQ== Message-ID: <29442561-9426-4635-9b7c-cdd138076127@kernel.org> Date: Tue, 31 Mar 2026 22:04:52 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/sparse: fix BUILD_BUG_ON check for section map alignment To: Andrew Morton , Muchun Song Cc: Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Petr Tesarik , linux-mm@kvack.org, linux-kernel@vger.kernel.org, muchun.song@linux.dev References: <20260331113023.2068075-1-songmuchun@bytedance.com> <20260331125529.de4deb7b46239fb13e4be517@linux-foundation.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: <20260331125529.de4deb7b46239fb13e4be517@linux-foundation.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Stat-Signature: pqjm3x8f5twt4xecutmi7attyhqrwegn X-Rspamd-Queue-Id: B85811A0009 X-Rspam-User: X-HE-Tag: 1774987504-484046 X-HE-Meta: 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 7iPsPir3 xhSQYLYSXEq7EKXyeiZo2O0Y24obd+UkF+kheRD3vsDDXtKsM2rkHge/VUWQ2WigOE1SjKHpyRI5CoA6y1gpDYhMDBQwPvB5rV9Dp3qn0JGSjHqt+TXfxGt1j8SPzyMTKB1cVJCKoZkd86hRAL+938EYbQiQMgYyUFOOMxtknf41UXVU5nlUQvGPeUz6m67Vm58TIxrvdSF5kCyTFjzni6Di105qDkZjLp9bhtDJBD3RDFLs4TdgI20aerK509ivdNAnnDIM1JirermSLdQxym2ByhinlxScYq9ALwwCTfKjcXigQNP27kDK3XUNfUmmGnlsmFFvtJjFxzek= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/31/26 21:55, Andrew Morton wrote: > On Tue, 31 Mar 2026 19:30:23 +0800 Muchun Song wrote: > >> The comment in mmzone.h states that the alignment requirement >> is the minimum of PAGE_SHIFT and PFN_SECTION_SHIFT. However, the >> pointer arithmetic (mem_map - section_nr_to_pfn()) results in >> a byte offset scaled by sizeof(struct page). Thus, the actual >> alignment provided by the second term is PFN_SECTION_SHIFT + >> __ffs(sizeof(struct page)). >> >> Update the compile-time check and the mmzone.h comment to >> accurately reflect this mathematically guaranteed alignment by >> taking the minimum of PAGE_SHIFT and PFN_SECTION_SHIFT + >> __ffs(sizeof(struct page)). This avoids the issue of the check >> being overly restrictive on architectures like powerpc where >> PFN_SECTION_SHIFT alone is very small (e.g., 6). >> >> Also, remove the exhaustive per-architecture bit-width list from the >> comment; such details risk falling out of date over time and may >> inadvertently be left un-updated, while the existing BUILD_BUG_ON >> provides sufficient compile-time verification of the constraint. >> >> No runtime impact so far: SECTION_MAP_LAST_BIT happens to fit within >> the smaller limit on all existing architectures. > > Thanks. So this can fix the build on some arch/kconfig combinations? > > Do you think we should fix older kernels? > >> Fixes: def9b71ee651 ("include/linux/mmzone.h: fix explanation of lower bits in the SPARSEMEM mem_map pointer") > > Eight years ago so I'm going with "no". IIUC, there is nothing broken. Could only be revealed by some new architecture. So no stable :) -- Cheers, David