From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C4893489FB1; Thu, 10 Sep 2026 14:29:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789050559; cv=none; b=NMq43LY8+ZJhLla+RPIuz/k+tbQI8GcR1Lt3zipdEx//ItHPu5oOCLO4CGpVFgwVxUMbcbGZ0beLWpH3zy31klzfI2CyCszn4e2/gZLN+fhw/0jkQqRNiLP8QCuCt1goy8qaSqT91pafMFdNWpu/SaXqOpwuQNShzFxds5eJhXE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789050559; c=relaxed/simple; bh=TAOYR8njee2iwqwI0d4esXJMuuALxt6G0+X5gSu7Jtk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=W3cxVaureMPw7BReKHIQjJBp6S4eebPIZY6hopcBl2oITmuI0wJXcWKGbJ5eT0JtzxsFY4lB4e77kE5Ml1N7ueB78z2wPqteUkJe93+fSSae+zlf1kLOKreJgSHDHQuxvQF7CsttS8bnNnDh0M5GlMnnN289UkIbP1/D/oFZ+3E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=I/DKz63I; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="I/DKz63I" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7B7D71F00893; Thu, 10 Sep 2026 14:29:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789050557; bh=u57NC1k6Bqf0mo7Kdt9/SiH0AeFRP72u3trAgFtt4Ns=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=I/DKz63Io0owfDmvuXF1ij9DmOob8NZ36qEzesmm68JMcrvrYC1f9gjBLiqyS1NNR AtCUF797lcT2SlhbFdyyfPMwXX7BVth8RKdT6q/+2i2gr+l5ZkVvEhyUoGhVzOTBBE TPZQ+UX9U1okNoy8vHDfi6hfrlJ3BUiXuQoEfNuvUWkkawQ8KJOY8pC0J/xMqPhq+j TbjK+5Q+Rj30wCkFfkJfcmIkdzpJrAKsK9oJPvJ5RVpQbDI3w2BX3trSlemnHEe/3p 2JLdlKg1fVyDjQDOYsSmtD5VuIKY26NLB+G1PhOILay33McJMAqhXw32euDxhrsGEL +s4H7uJsegykQ== Message-ID: Date: Thu, 10 Sep 2026 16:29:06 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 08/12] mm/sparse: move __highest_used_section_nr handling To: "Lorenzo Stoakes (ARM)" Cc: Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kairui Song , Qi Zheng , Shakeel Butt , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , Brendan Jackman , Johannes Weiner , Zi Yan , Oscar Salvador , Greg Kroah-Hartman , "Rafael J. Wysocki" , Danilo Krummrich , Jan Kiszka , Kieran Bingham , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-cxl@vger.kernel.org, driver-core@lists.linux.dev, linux-fsdevel@vger.kernel.org References: <20260909-b4-sparsemem_cleanups-v1-0-008fc8d579fe@kernel.org> <20260909-b4-sparsemem_cleanups-v1-8-008fc8d579fe@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 Content-Transfer-Encoding: 7bit On 9/10/26 16:16, Lorenzo Stoakes (ARM) wrote: > On Wed, Sep 09, 2026 at 03:33:01PM +0200, David Hildenbrand (Arm) wrote: >> Let's move it to sparse_init_one_section(). However, to keep early >> boot processing working, we also have to initialize it in >> sparse_sections_init(). > > A why might be nice :) Agreed, I'll mention that. > > I guess preparing for removal of __section_mark_present()? > Right intuition :) > Also good to have arguments as to why this is equivalent of previous > behaviour. > > E.g. higher pfn = higher section nr so naturally the highest is the one you > end up wtih at the end of sparse_sections_init()? We go over all sections, just earlier. > >> >> Should we use READ_ONCE/WRITE_ONCE with __highest_used_section_nr? >> Probably, something for another day. > > It might be worth expanding this a bit. Do multiple threads read/write this > concurrently? Hah, I'll probably just drop it. I was just stumbling over readers vs. concurrent updates and thought "that looks suspicious". > > No functional change intended here or is one intended? :) > Certainly no change intended ;) > Before it was: > > mm_core_init_early() -> sparse_sections_init() -> __section_mark_present() > sparse_add_section() -> __section_mark_present() > > Now: > > mm_core_init_early() -> sparse_sections_init() [early] > sparse_add_section() -> sparse_init_one_section() > > But also called from mm_core_init_early(): > > sparse_init() -> sparse_metadata_init() -> sparse_metadata_init_nid() -> sparse_init_one_section() > > Are both required? sparse_metadata_init() relies on __highest_used_section_nr in the for_each_early_section_nr / for_each_present_section_nr, so it is required. I could probable move the update on the hotplug side into sparse_add_section() instead! > > >> >> Signed-off-by: David Hildenbrand (Arm) >> --- >> mm/sparse.c | 5 +++-- >> mm/sparse.h | 6 +++--- >> 2 files changed, 6 insertions(+), 5 deletions(-) >> >> diff --git a/mm/sparse.c b/mm/sparse.c >> index 2b41ae36f20b8..2d0f2db34f4cf 100644 >> --- a/mm/sparse.c >> +++ b/mm/sparse.c >> @@ -177,7 +177,7 @@ static inline unsigned long first_present_section_nr(void) >> >> void __init sparse_sections_init(void) >> { >> - unsigned long pfn, start_pfn, end_pfn; >> + unsigned long pfn, start_pfn, end_pfn, section_nr; >> int i, nid; >> >> sparse_extreme_init(); >> @@ -187,9 +187,9 @@ void __init sparse_sections_init(void) >> mminit_validate_memmodel_limits(&start_pfn, &end_pfn); >> >> for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) { >> - unsigned long section_nr = pfn_to_section_nr(pfn); >> struct mem_section *ms; >> >> + section_nr = pfn_to_section_nr(pfn); >> sparse_index_init(section_nr, nid); >> ms = __nr_to_section(section_nr); >> if (ms->section_mem_map) >> @@ -201,6 +201,7 @@ void __init sparse_sections_init(void) >> __section_mark_present(ms, section_nr); >> } >> } >> + __highest_used_section_nr = section_nr; >> } >> >> #ifndef CONFIG_SPARSEMEM_VMEMMAP >> diff --git a/mm/sparse.h b/mm/sparse.h >> index 7c5d82ceb7142..a3af4967fd5c5 100644 >> --- a/mm/sparse.h >> +++ b/mm/sparse.h >> @@ -97,6 +97,9 @@ static inline void sparse_init_one_section(struct mem_section *ms, >> >> BUILD_BUG_ON(SECTION_MAP_LAST_BIT > PFN_SECTION_SHIFT); >> >> + if (section_nr > __highest_used_section_nr) >> + __highest_used_section_nr = section_nr; >> + > > Could also be: > > section_nr = max(section_nr, __highest_used_section_nr); Ack! -- Cheers, David