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 A088D381EBA for ; Fri, 7 Aug 2026 11:25:25 +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=1786101926; cv=none; b=NsmSGhg9ic6cWSzXc3Nfl5qBLoiEMDuzBIXIMeU8g0S3aCWcC0J1eK1dfYVWQ0JiQkKknTyeHOZ8GVyrPOmXQdSVjtZQRNZQ12OC6LluzT1zU2qbd/UC1VGrcKOPPKd4KdqM/CAgqk5P9t5m0+e8INyaW7gDF2qgVqBc3ACGV2c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786101926; c=relaxed/simple; bh=OgOwYXslsOGYvf41LL4q+ML/3bMYkg5pxFOkXgQGvLQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=IlTQqBXHrrPSfOg4Oy1dQNtQXKkNO6RBsDIA7Bz+DQ40IfSmFfDRVQFleXJXZhNt5m+y9+0I0AlguywS1mcEOgdqwd1kMlcY/Nv4p2wzVHluXioh3qOgYyxs2LAXKwMFEIsd6M/cpqF6SUJ7SmEnC4lx8bsQf748tz1TQ+nOyb8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=NvusTGEl; 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="NvusTGEl" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3C3631F00A3A; Fri, 7 Aug 2026 11:25:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786101925; bh=p9g/3Te/DMFHNFPb4/a0KQzBfiLfVixcDYjY5aWEY8w=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=NvusTGElGc15NdCe6mq7jvl8yLc7zLopyx8UbB+CZrfb65Qb1e75iWo297AFC7XlQ Fy2xdG7WvrmFgs2zq5t4g2/IPIdQC5O9ezNn9euxKMG5qAFQ5mbe6iyUey8U8ck/91 rmd0ak1G7ieSu9a2734ItLITpZL5k5RUxsW1JKziGteJU/d1Cg8xbUlVbFHjWJo2sU N1o9iK6RgRB7kPOOLB4mvTbr2f/01HD1q335jV53pSPh5tBsM0nWJZtbBCd+zdc4PL 6Qr421mbamMmmMV8YeSOApwyMT8CXzNBK7QkhajnFv6ca8Sr45Ibgmn+BnJPhdWDaH AHaoHELbxhFhA== Message-ID: Date: Fri, 7 Aug 2026 13:25:20 +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 v6 2/2] mm/memory_hotplug: improve shrink_zone_span() subsection boundary checks To: Wei Yang Cc: Yuan Liu , Oscar Salvador , Mike Rapoport , linux-mm@kvack.org, Nanhai Zou , Pan Deng , Tianyou Li , Chen Zhang , Jason Zeng , linux-kernel@vger.kernel.org References: <20260723084946.189392-1-yuan1.liu@intel.com> <20260723084946.189392-3-yuan1.liu@intel.com> <20260807032205.ykhxbapx6nhg5hpt@master> 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: <20260807032205.ykhxbapx6nhg5hpt@master> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/7/26 05:22, Wei Yang wrote: > On Wed, Aug 05, 2026 at 01:02:29PM +0200, David Hildenbrand (Arm) wrote: >> On 7/23/26 10:49, Yuan Liu wrote: >>> When shrinking a zone span after removing a PFN range, >>> find_smallest_section_pfn() and find_biggest_section_pfn() >>> only checked one edge PFN in each subsection for nid/zone matching. >>> >>> If a memory or hole boundary falls in the middle of a subsection, >>> that edge PFN may belong to a different nid/zone, causing the helpers >>> to miss a valid PFN within that subsection. >>> >>> Fix this by checking both subsection edge PFNs for nid/zone matching. >>> Keep a single pfn_to_online_page() check per subsection, since online >>> state is the same for all PFNs in a subsection. >>> >>> Reviewed-by: Jason Zeng >>> Signed-off-by: Yuan Liu >>> --- >>> mm/memory_hotplug.c | 42 +++++++++++++++++++++++++++--------------- >>> 1 file changed, 27 insertions(+), 15 deletions(-) >>> >>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >>> index 4c699fd9c479..3a281d595207 100644 >>> --- a/mm/memory_hotplug.c >>> +++ b/mm/memory_hotplug.c >>> @@ -427,17 +427,24 @@ static unsigned long find_smallest_section_pfn(int nid, struct zone *zone, >>> unsigned long start_pfn, >>> unsigned long end_pfn) >>> { >>> - for (; start_pfn < end_pfn; start_pfn += PAGES_PER_SUBSECTION) { >>> - if (unlikely(!pfn_to_online_page(start_pfn))) >>> - continue; >>> + unsigned long next_pfn; >>> >>> - if (unlikely(pfn_to_nid(start_pfn) != nid)) >>> - continue; >>> + for (; start_pfn < end_pfn; start_pfn = next_pfn) { >>> + unsigned long tail_pfn; >>> >>> - if (zone != page_zone(pfn_to_page(start_pfn))) >>> + next_pfn = start_pfn + PAGES_PER_SUBSECTION; >>> + tail_pfn = next_pfn - 1; >>> + >>> + if (unlikely(!pfn_to_online_page(start_pfn))) >>> continue; >>> >>> - return start_pfn; >>> + if (likely(pfn_to_nid(start_pfn) == nid) && >>> + zone == page_zone(pfn_to_page(start_pfn))) >>> + return start_pfn; >>> + >>> + if (likely(pfn_to_nid(tail_pfn) == nid) && >>> + zone == page_zone(pfn_to_page(tail_pfn))) >>> + return start_pfn; >>> } >>> >>> return 0; >>> @@ -448,21 +455,26 @@ static unsigned long find_biggest_section_pfn(int nid, struct zone *zone, >>> unsigned long start_pfn, >>> unsigned long end_pfn) >>> { >>> - unsigned long pfn; >>> + unsigned long pfn, prev_pfn; >>> >>> /* pfn is the end pfn of a memory section. */ >>> pfn = end_pfn - 1; >>> - for (; pfn >= start_pfn; pfn -= PAGES_PER_SUBSECTION) { >>> - if (unlikely(!pfn_to_online_page(pfn))) >>> - continue; >>> + for (; pfn >= start_pfn; pfn = prev_pfn) { >>> + unsigned long head_pfn; >>> >>> - if (unlikely(pfn_to_nid(pfn) != nid)) >>> - continue; >>> + prev_pfn = pfn - PAGES_PER_SUBSECTION; >>> + head_pfn = prev_pfn + 1; >>> >>> - if (zone != page_zone(pfn_to_page(pfn))) >>> + if (unlikely(!pfn_to_online_page(pfn))) >>> continue; >>> >>> - return pfn; >>> + if (likely(pfn_to_nid(pfn) == nid) && >>> + zone == page_zone(pfn_to_page(pfn))) >>> + return pfn; >>> + >>> + if (likely(pfn_to_nid(head_pfn) == nid) && >>> + zone == page_zone(pfn_to_page(head_pfn))) >>> + return pfn; >>> } >>> >>> return 0; >> >> >> I think improving that should be patch #1. >> >> But I think we can do much better code-wise. What about the following >> cleanup instead: >> >> >> >From 6e9ea094daf8d04c0b119b780572a846334f8164 Mon Sep 17 00:00:00 2001 >> From: "David Hildenbrand (Arm)" >> Date: Wed, 5 Aug 2026 12:52:55 +0200 >> Subject: [PATCH] mm/memory_hotplug: make shrink_zone_span() more robust >> >> Let's make shrink_zone_span() more robust by checking in >> find_smallest_section_pfn() / find_biggest_section_pfn() that start+end >> of the subsection. >> >> While at it, clean up the function heavily, factoring the core check >> out into subsection_overlaps_zone(). >> >> There likely is no need to check for the nid first: we require >> SPARSEMEM_VMEMMAP_ENABLE where pfn_to_page() is cheap, and the >> pfn_to_nid() on CONFIG_NUMA would do a pfn_to_page() either way. So >> let's just drop that for now. >> >> Signed-off-by: David Hildenbrand (Arm) >> --- >> mm/memory_hotplug.c | 59 ++++++++++++++++++--------------------------- >> 1 file changed, 24 insertions(+), 35 deletions(-) >> >> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >> index 226ab9cb078ad..79937f9672d01 100644 >> --- a/mm/memory_hotplug.c >> +++ b/mm/memory_hotplug.c >> @@ -425,49 +425,39 @@ int __add_pages(int nid, unsigned long pfn, unsigned long nr_pages, >> return err; >> } >> >> -/* find the smallest valid pfn in the range [start_pfn, end_pfn) */ >> -static unsigned long find_smallest_section_pfn(int nid, struct zone *zone, >> - unsigned long start_pfn, >> - unsigned long end_pfn) >> +static bool subsection_overlaps_zone(unsigned long pfn, struct zone *zone) >> { >> - for (; start_pfn < end_pfn; start_pfn += PAGES_PER_SUBSECTION) { >> - if (unlikely(!pfn_to_online_page(start_pfn))) >> - continue; >> + const unsigned long start_pfn = ALIGN_DOWN(pfn, PAGES_PER_SUBSECTION); >> + const unsigned long end_pfn = start_pfn + PAGES_PER_SUBSECTION - 1; >> >> - if (unlikely(pfn_to_nid(start_pfn) != nid)) >> - continue; >> + /* All pages in a subsection are either online or offline. */ >> + if (unlikely(!pfn_to_online_page(start_pfn))) >> + return false; >> >> - if (zone != page_zone(pfn_to_page(start_pfn))) >> - continue; >> + /* Checking start+end is sufficient. */ >> + return zone == page_zone(pfn_to_page(start_pfn)) || >> + zone == page_zone(pfn_to_page(end_pfn)); >> +} > > Hi, David Hi, > > I am thinking if we could initialize each subsection to only one zone, we may > reduce the complexity? > > For example, in init_unavailable_range() align spfn to subsection and init the > head unaligned part to previous zone? > > Do you think this is reasonable? I'm afraid of opening up another can of worms. :) The additional page_zone(pfn_to_page(end_pfn) check is cheap with VMEMMAP, so I think we should focus on that first. (and the patch is in general a cleanup :) ) -- Cheers, David