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b=Oja3AqjsW5GP/6tkHzvlIoS8mBTOp9Du3zT1sP+oFAXBoPJgYZiZlPy6BKP1fIzG7 ZrbiiwArmjzPeGpRKKO+KX0PXwNzcbPI1lPt9g29p/qJs5I+gGw1wP8d6BE2g+2+TY aRxl2P6GwL+f9MqYsqf6NmYZa7rro1x+uomRN9XcjvK0uce8+Pa7j3xjQNvV9W5lbH R61z94B+48hGYhgEfqDoW0M01M1NHw9xJ1glcQAGo2buzoSBWJAAgdoMrylMFP42Qt X5uE8II/tBHfCBwVaExiVDj65+4NI8EKHXQFGhQjPQgdiQWimBYxGxnNc1sRTTV/8N 8GY3xC5kpoImA== Message-ID: Date: Fri, 27 Mar 2026 16:28:53 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/memory_hotplug: maintain N_NORMAL_MEMORY during hotplug To: Joshua Hahn , Hao Li Cc: osalvador@suse.de, akpm@linux-foundation.org, vbabka@suse.cz, harry.yoo@oracle.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-cxl@vger.kernel.org References: <20260327143823.3063541-1-joshua.hahnjy@gmail.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: <20260327143823.3063541-1-joshua.hahnjy@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 58EAA80005 X-Stat-Signature: t1oy1ct6478dmzgyaekg8tjfqesg9aqr X-Rspamd-Server: rspam06 X-HE-Tag: 1774625338-944263 X-HE-Meta: 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 cd4qIPw+ tXLA5J35cLad0oui8SwZqoVTtD+Rt5aLvQCTNj6Sse1o2OYihiYgB167SJs2BF37WpkE41spwgdJJYKVWOUEjp+F1sfs/GCCEY5z/9y0vPFV3bQvmSUDkEmkRWKBjTB2Nqyg5o7fmzIPZqfOqZ2U0dy0pFQw9NnSN0Ms9R3I0Edo08B9ZknWkBYeek/kwSZtcZFhm80acpEVnJZC91KHzC4YmkSYI9vYhXMXFfvqdu8mfJs9ZIVa9qovxArUQBrC0E3aHkqYq1sJD4PgPKZmidaLkMeLfQvSH9x6sua4DN2N51Gp2bdbZTTTFkMt0IbKuOpeK8KIMLQtzhWGTQDuQADGdXQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/27/26 15:38, Joshua Hahn wrote: > On Fri, 27 Mar 2026 20:42:47 +0800 Hao Li wrote: > > Hello Hao, > > I hope you are doing well, thank you for the patch! > >> N_NORMAL_MEMORY is initialized from zone population at boot, but memory >> hotplug currently only updates N_MEMORY. As a result, a node that gains >> normal memory via hotplug can remain invisible to users iterating over >> N_NORMAL_MEMORY, while a node that loses its last normal memory can stay >> incorrectly marked as such. > > The second part feels more important than the second part, doing a quick > glance through the code I can see a few N_NORMAL_MEMORY iterators that > are in some hot paths like shrink_memcg. Iterating over nodes that don't > contain any NORMAL memory seems like an inefficiency rather than a bug > though. > >> Restore N_NORMAL_MEMORY maintenance directly in online_pages() and >> offline_pages(). Set the bit when a node that currently lacks normal >> memory onlines pages into a zone <= ZONE_NORMAL, and clear it when >> offlining removes the last present pages from zones <= ZONE_NORMAL. >> >> This restores the intended semantics without bringing back the old >> status_change_nid_normal notifier plumbing which was removed in >> 8d2882a8edb8. >> >> Current users that benefit include list_lru, zswap, nfsd filecache, >> hugetlb_cgroup, and has_normal_memory sysfs reporting. >> >> Signed-off-by: Hao Li >> --- >> >> This patch also prepares for a subsequent SLUB change that makes >> can_free_to_pcs() rely on N_NORMAL_MEMORY to decide whether an object can be >> freed to the sheaf. >> >> --- >> mm/memory_hotplug.c | 22 ++++++++++++++++++++++ >> 1 file changed, 22 insertions(+) >> >> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >> index bc805029da51..5498744aa1f1 100644 >> --- a/mm/memory_hotplug.c >> +++ b/mm/memory_hotplug.c >> @@ -1155,6 +1155,7 @@ int online_pages(unsigned long pfn, unsigned long nr_pages, >> int need_zonelists_rebuild = 0; >> unsigned long flags; >> int ret; >> + bool need_set_normal_memory = false; >> >> /* >> * {on,off}lining is constrained to full memory sections (or more >> @@ -1180,6 +1181,9 @@ int online_pages(unsigned long pfn, unsigned long nr_pages, >> if (ret) >> goto failed_addition; >> } >> + /* Adding normal memory to the node for the first time */ >> + if (!node_state(nid, N_NORMAL_MEMORY) && zone_idx(zone) <= ZONE_NORMAL) >> + need_set_normal_memory = true; >> >> ret = memory_notify(MEM_GOING_ONLINE, &mem_arg); >> ret = notifier_to_errno(ret); >> @@ -1209,6 +1213,8 @@ int online_pages(unsigned long pfn, unsigned long nr_pages, >> >> if (node_arg.nid >= 0) >> node_set_state(nid, N_MEMORY); >> + if (need_set_normal_memory) >> + node_set_state(nid, N_NORMAL_MEMORY); >> if (need_zonelists_rebuild) >> build_all_zonelists(NULL); > > Do we need the flag here? As far as I can tell, we can just skip this and just > directly check whether this is the first normal memory we are adding to the > node here and set the bit. Then we can remove the flag and the extraneous > check. We won't do any notifier work so I think it should be OK. I assume you simply mean: if (zone_idx(zone) <= ZONE_NORMAL && !node_state(nid, N_NORMAL_MEMORY)) node_set_state(nid, N_NORMAL_MEMORY); That looks m uch better! > >> @@ -1908,6 +1914,9 @@ int offline_pages(unsigned long start_pfn, unsigned long nr_pages, >> unsigned long flags; >> char *reason; >> int ret; >> + bool need_clear_normal_memory = false; >> + unsigned long node_normal_pages = 0; >> + enum zone_type zt; >> >> /* >> * {on,off}lining is constrained to full memory sections (or more >> @@ -1977,6 +1986,13 @@ int offline_pages(unsigned long start_pfn, unsigned long nr_pages, >> goto failed_removal_isolated; >> } >> } >> + /* >> + * Check whether this operation removes the node's last normal memory. >> + */ >> + for (zt = 0; zt <= ZONE_NORMAL; zt++) >> + node_normal_pages += pgdat->node_zones[zt].present_pages; >> + if (nr_pages >= node_normal_pages && zone_idx(zone) <= ZONE_NORMAL) >> + need_clear_normal_memory = true; >> >> ret = memory_notify(MEM_GOING_OFFLINE, &mem_arg); >> ret = notifier_to_errno(ret); >> @@ -2055,6 +2071,12 @@ int offline_pages(unsigned long start_pfn, unsigned long nr_pages, >> /* reinitialise watermarks and update pcp limits */ >> init_per_zone_wmark_min(); > > Same here, couldn't we just iterate through the paegs here and accumulate > node_normal_pages and clear the memory here? We can get rid of the bool and > also keep node_normal_pages defined inside an if (zone_idx(zone) <= ZONE_NORMAL) > check as well. Right, all we have to do is check for remaining present_pages in one of the nodes IIUC. -- Cheers, David