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b=WEYZtYIUGsoIkaVTqDPKbWrAK9lstxF2JzJqxaCr8Xihvl4mgDHxpPep9VRR2oBHP cLdiOgPax8aSFLcLjYi2a/Os+MVPqUm7MZLsVr8UXg4+RJSTc4xh0Pvt1H8vyF2lyC mxn9Qh+DvlcI2wn/cz/aqw9dEpYN7/1eajSPrdCQ= Date: Mon, 22 Dec 2025 17:15:12 -0800 From: Andrew Morton To: Yuan Liu Cc: baolu.lu@linux.intel.com, david@redhat.com, rppt@kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] mm: fix huge page table not free after memory unplug Message-Id: <20251222171512.edfb1e839e3f007d89825363@linux-foundation.org> In-Reply-To: <20251222041117.44865-1-yuan1.liu@intel.com> References: <20251222041117.44865-1-yuan1.liu@intel.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: CA72540002 X-Rspamd-Server: rspam10 X-Stat-Signature: m5kfsyg4pty1gmn35psjr4tmgue933b5 X-HE-Tag: 1766452514-92826 X-HE-Meta: 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 lgCYdkeX kSRsHTglYp9VSiPP3ar7eHl+OFIc2ezGXGi10NR++9oJzp5mMgSx4ClOiH0lZecs45C31Galw7K+oZPo9PfPw8ykxEX1H6qZnIMTK9KQg5cgFxTgNCUVx5jNHKHgMYphhSFm90PXzXotzuRjAgBzpsdIBko+Sm37oavDW6g6ljJ14bSzU2hxdeFHiKPKy3M3k7z0EgfHJdpZ9FPjIIOPHd+uprvkgZF9b16FWexL/sANWZLh8opn2Ar47+cyVm2OB0h57J0QPRmy5KlA= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, 21 Dec 2025 23:11:17 -0500 Yuan Liu wrote: > newly plugged memory is marked as prot_sethuge via phys_pmd_init > without setting PG_head. During memory unplug, free_hugepage_table > frees the page table as 2M, but pagetable_free handles it as 4K. > > The following test case of memory unplug for a VM [1], tested in > the environment [2], show that results. > > +-----------------------+------+------+ > |Check System Memory |Plug |Unplug| > |via free -h |256GB |256GB | > +-----------------------+------+------+ > | Free 4K page table |257GB |5.6GB | > +-----------------------+------+------+ > | Free 2M page table |257GB |1.7GB | > +-----------------------+------+------+ > > [1] Qemu commands to unhotplug 256G memory for a VM: > object_add memory-backend-ram,id=hotmem0,size=256G,share=on > device_add virtio-mem-pci,id=vmem1,memdev=hotmem0,bus=port1 > qom-set vmem1 requested-size 256G (Plug Memory) > qom-set vmem1 requested-size 0G (Unplug Memory) > > [2] Hardware : Intel Icelake server > Guest Kernel : v6.19-rc1 > 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 > > ... > > --- a/arch/x86/mm/init_64.c > +++ b/arch/x86/mm/init_64.c > @@ -1028,7 +1028,7 @@ static void __meminit free_pagetable(struct page *page, int order) > free_reserved_pages(page, nr_pages); > #endif > } else { > - pagetable_free(page_ptdesc(page)); > + __free_pages(page, order); > } > } This reverts half of bf9e4e30f353 ("x86/mm: use pagetable_free()"). What about the other half? The below change that patch made to arch/x86/mm/pat/set_memory.c - is that OK? --- a/arch/x86/mm/pat/set_memory.c +++ b/arch/x86/mm/pat/set_memory.c @@ -429,7 +429,7 @@ static void cpa_collapse_large_pages(struct cpa_data *cpa) list_for_each_entry_safe(ptdesc, tmp, &pgtables, pt_list) { list_del(&ptdesc->pt_list); - __free_page(ptdesc_page(ptdesc)); + pagetable_free(ptdesc); } }