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b=tIUHmfcliQiRyYv+4RxvHKh5zUVWOvlz9N1GJoHIWYmp/53VyeTZ/5Ys34S7aTQBi ju8h66ch2EbJCr7Fqw93Y7S5JK4hWEQJJUIK3x0FOpp0uzGEJBzdYYcampYKFYjJB8 SvX2GZTBlHkepW3lNV2H3R6cus4MWC8DUxgvi3Eheh0S4+x60lVSZYjAhQG7QWRLOj QTd6jqYQkJzvyMC1mvmZ+d7symxwkCHMMKqB7eYMITgpf+Cjdxk6jYPvmZcAa1dWaN AmS2BQ5susZRgzcotybX5LvBXS7sMNMtSOXiUS2ypW8CTcx2eXrZtIIpbJOwvi8tOr sDcFygQx1DCAg== Message-ID: Date: Thu, 9 Apr 2026 17:08:18 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm/memory hotplug/unplug: Optimize zone contiguous check when changing pfn range To: Mike Rapoport Cc: Yuan Liu , Oscar Salvador , Wei Yang , linux-mm@kvack.org, Yong Hu , Nanhai Zou , Tim Chen , Qiuxu Zhuo , Yu C Chen , Pan Deng , Tianyou Li , Chen Zhang , linux-kernel@vger.kernel.org References: <20260408031615.1831922-1-yuan1.liu@intel.com> <17b821b6-0176-43d5-92f7-fe2a0c4f70cf@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 X-Rspamd-Queue-Id: 92C2C40011 X-Stat-Signature: b1op5pxry4x6eefoq93ce7oypa4nijtx X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1775747305-861495 X-HE-Meta: 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 jv31e/75 muaXOvAp9nXxapcDtxkH5iHrfcRaSuQZlRDovkTjUX0jVJnkTyg5w40frlyL+bkjcWe5crvieWg7AytEq5s+SpcpDCbTUf5dwe0KB9hu/oY+F032QEEWWDrdky8akiVOVff8egtSPrZzQ4969U73wmvk/MYzH8EqGDNqUWdSyxrS3Z9g6PS/Uq0d6QCRFejWTBqks+q7dcv0+nYgCSylT7PP7wRFM0wWZuqoISa5haHL1CtNB5ZsOoDpBGiGdqKDboqDmWo1+2SdbNC7CQvjzBT0XplF6mD7dIGKp7fRLN20X/jVZ2sDagdQtSbeXTOTMVmeRGhAbCQmq0SVtDbKuZvE1KXsneeNgs2GNKl2VdZuOEb+MrHaA5ud/vf2xrwo3547z8ViO9O9VE03p5qgMSM1XFFyWIpElBIC42mpJxnC5cnuiPat22EZxc+zOKCWdzfNbVl4kbgRaITw= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/9/26 16:40, Mike Rapoport wrote: > On Wed, Apr 08, 2026 at 09:36:14AM +0200, David Hildenbrand (Arm) wrote: >> On 4/8/26 05:16, Yuan Liu wrote: >>> When move_pfn_range_to_zone() or remove_pfn_range_from_zone() updates a >>> zone, set_zone_contiguous() rescans the entire zone pageblock-by-pageblock >>> to rebuild zone->contiguous. For large zones this is a significant cost >>> during memory hotplug and hot-unplug. >>> >>> Add a new zone member pages_with_online_memmap that tracks the number of >>> pages within the zone span that have an online memory map (including present >>> pages and memory holes whose memory map has been initialized). When >>> spanned_pages == pages_with_online_memmap the zone is contiguous and >>> pfn_to_page() can be called on any PFN in the zone span without further >>> pfn_valid() checks. >>> >>> Only pages that fall within the current zone span are accounted towards >>> pages_with_online_memmap. A "too small" value is safe, it merely prevents >>> detecting a contiguous zone. >>> >>> The following test cases of memory hotplug for a VM [1], tested in the >>> environment [2], show that this optimization can significantly reduce the >>> memory hotplug time [3]. >>> >>> +----------------+------+---------------+--------------+----------------+ >>> | | Size | Time (before) | Time (after) | Time Reduction | >>> | +------+---------------+--------------+----------------+ >>> | Plug Memory | 256G | 10s | 3s | 70% | >>> | +------+---------------+--------------+----------------+ >>> | | 512G | 36s | 7s | 81% | >>> +----------------+------+---------------+--------------+----------------+ >>> >>> +----------------+------+---------------+--------------+----------------+ >>> | | Size | Time (before) | Time (after) | Time Reduction | >>> | +------+---------------+--------------+----------------+ >>> | Unplug Memory | 256G | 11s | 4s | 64% | >>> | +------+---------------+--------------+----------------+ >>> | | 512G | 36s | 9s | 75% | >>> +----------------+------+---------------+--------------+----------------+ >>> >>> [1] Qemu commands to hotplug 256G/512G memory for a VM: >>> object_add memory-backend-ram,id=hotmem0,size=256G/512G,share=on >>> device_add virtio-mem-pci,id=vmem1,memdev=hotmem0,bus=port1 >>> qom-set vmem1 requested-size 256G/512G (Plug Memory) >>> qom-set vmem1 requested-size 0G (Unplug Memory) >>> >>> [2] Hardware : Intel Icelake server >>> Guest Kernel : v7.0-rc4 >>> Qemu : v9.0.0 >>> >>> Launch VM : >>> qemu-system-x86_64 -accel kvm -cpu host \ >>> -drive file=./Centos10_cloud.qcow2,format=qcow2,if=virtio \ >>> -drive file=./seed.img,format=raw,if=virtio \ >>> -smp 3,cores=3,threads=1,sockets=1,maxcpus=3 \ >>> -m 2G,slots=10,maxmem=2052472M \ >>> -device pcie-root-port,id=port1,bus=pcie.0,slot=1,multifunction=on \ >>> -device pcie-root-port,id=port2,bus=pcie.0,slot=2 \ >>> -nographic -machine q35 \ >>> -nic user,hostfwd=tcp::3000-:22 >>> >>> Guest kernel auto-onlines newly added memory blocks: >>> echo online > /sys/devices/system/memory/auto_online_blocks >>> >>> [3] The time from typing the QEMU commands in [1] to when the output of >>> 'grep MemTotal /proc/meminfo' on Guest reflects that all hotplugged >>> memory is recognized. >>> >>> Reported-by: Nanhai Zou >>> Reported-by: Chen Zhang >>> Tested-by: Yuan Liu >>> Reviewed-by: Tim Chen >>> Reviewed-by: Qiuxu Zhuo >>> Reviewed-by: Yu C Chen >>> Reviewed-by: Pan Deng >>> Reviewed-by: Nanhai Zou >>> Co-developed-by: Tianyou Li >>> Signed-off-by: Tianyou Li >>> Signed-off-by: Yuan Liu >>> Acked-by: David Hildenbrand (Arm) >>> --- >> >> [...] >> >>> @@ -842,7 +842,7 @@ overlap_memmap_init(unsigned long zone, unsigned long *pfn) >>> * zone/node above the hole except for the trailing pages in the last >>> * section that will be appended to the zone/node below. >>> */ >>> -static void __init init_unavailable_range(unsigned long spfn, >>> +static unsigned long __init init_unavailable_range(unsigned long spfn, >>> unsigned long epfn, >>> int zone, int node) >>> { >>> @@ -858,6 +858,7 @@ static void __init init_unavailable_range(unsigned long spfn, >>> if (pgcnt) >>> pr_info("On node %d, zone %s: %lld pages in unavailable ranges\n", >>> node, zone_names[zone], pgcnt); >>> + return pgcnt; >>> } >>> >>> /* >>> @@ -956,9 +957,22 @@ static void __init memmap_init_zone_range(struct zone *zone, >>> memmap_init_range(end_pfn - start_pfn, nid, zone_id, start_pfn, >>> zone_end_pfn, MEMINIT_EARLY, NULL, MIGRATE_MOVABLE, >>> false); >>> + zone->pages_with_online_memmap += end_pfn - start_pfn; >>> >>> - if (*hole_pfn < start_pfn) >>> - init_unavailable_range(*hole_pfn, start_pfn, zone_id, nid); >>> + if (*hole_pfn < start_pfn) { >>> + unsigned long pgcnt; >>> + >>> + if (*hole_pfn < zone_start_pfn) { >>> + init_unavailable_range(*hole_pfn, zone_start_pfn, >>> + zone_id, nid); >>> + pgcnt = init_unavailable_range(zone_start_pfn, >>> + start_pfn, zone_id, nid); >> >> Indentation of parameters. >> >>> + } else { >>> + pgcnt = init_unavailable_range(*hole_pfn, start_pfn, >>> + zone_id, nid); >> >> >> Same here. >> >>> + } >>> + zone->pages_with_online_memmap += pgcnt; >>> + } >> >> >> Maybe something like the following could make it nicer to read, just a >> thought. >> >> >> unsigned long hole_start_pfn = *hole_pfn; >> >> if (hole_start_pfn < zone_start_pfn) { >> init_unavailable_range(hole_start_pfn, zone_start_pfn, >> zone_id, nid); >> hole_start_pfn = zone_start_pfn; >> } >> pgcnt = init_unavailable_range(hole_start_pfn, start_pfn, >> zone_id, nid); >> > > Yeah, this looks better :) > > sashiko had several comments > https://sashiko.dev/#/patchset/20260408031615.1831922-1-yuan1.liu%40intel.com > > I skipped the ones related to hotplug, but in the mm_init part the comment > about zones that can have overlapping physical spans when mirrored > kernelcore is enabled seems valid. The set_zone_contiguous/clear_zone_contiguous can be ignored I think. The comment about shrink_zone_span() is likely not realistic. shrink_zone_span() would not shrink over boot holes. Well, unless we have an odd case where the hole+memory starts in the middle of a "PAGES_PER_SUBSECTION". That would already be problematic if memory starts/ends in the middle of a PAGES_PER_SUBSECTION chunk. I don't such a case exists. We could improve shrink_zone_span() to let find_smallest_section_pfn/find_biggest_section_pfn test the pfn_to_nid() and page_zone() not on;y on the smallest/highest pfn, but also on the highest/smallest PFN in a PAGES_PER_SUBSECTION chunk. No need to test pfn_to_online_page() twice, as that is the same result for all pages in a PAGES_PER_SUBSECTION chunk. -- Cheers, David