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[2003:cb:c708:1a00:df86:93fe:6505:d096]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-42905971ad7sm35137405e9.17.2024.08.07.08.23.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 07 Aug 2024 08:23:50 -0700 (PDT) Message-ID: <936f8adf-a8a5-45eb-b5a3-297773918f7c@redhat.com> Date: Wed, 7 Aug 2024 17:23:48 +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 2/2] mm: keep nid around during hot-remove To: Pasha Tatashin Cc: agordeev@linux.ibm.com, akpm@linux-foundation.org, alexghiti@rivosinc.com, aou@eecs.berkeley.edu, ardb@kernel.org, arnd@arndb.de, bhe@redhat.com, bjorn@rivosinc.com, borntraeger@linux.ibm.com, bp@alien8.de, catalin.marinas@arm.com, chenhuacai@kernel.org, chenjiahao16@huawei.com, christophe.leroy@csgroup.eu, dave.hansen@linux.intel.com, dawei.li@shingroup.cn, gerald.schaefer@linux.ibm.com, gor@linux.ibm.com, hca@linux.ibm.com, hpa@zytor.com, kent.overstreet@linux.dev, kernel@xen0n.name, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, loongarch@lists.linux.dev, luto@kernel.org, maobibo@loongson.cn, mark.rutland@arm.com, mcgrof@kernel.org, mingo@redhat.com, mpe@ellerman.id.au, muchun.song@linux.dev, namcao@linutronix.de, naveen@kernel.org, npiggin@gmail.com, osalvador@suse.de, palmer@dabbelt.com, paul.walmsley@sifive.com, peterz@infradead.org, philmd@linaro.org, rdunlap@infradead.org, rientjes@google.com, rppt@kernel.org, ryan.roberts@arm.com, souravpanda@google.com, svens@linux.ibm.com, tglx@linutronix.de, tzimmermann@suse.de, will@kernel.org, x86@kernel.org References: <20240806221454.1971755-1-pasha.tatashin@soleen.com> <20240806221454.1971755-2-pasha.tatashin@soleen.com> <345ba221-e094-47e8-9481-562faf4acd85@redhat.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 07.08.24 16:40, Pasha Tatashin wrote: > On Wed, Aug 7, 2024 at 7:50 AM David Hildenbrand wrote: >> >> On 07.08.24 13:32, David Hildenbrand wrote: >>> On 07.08.24 00:14, Pasha Tatashin wrote: >>>> nid is needed during memory hot-remove in order to account the >>>> information about the memmap overhead that is being removed. >>>> >>>> In addition, we cannot use page_pgdat(pfn_to_page(pfn)) during >>>> hotremove after remove_pfn_range_from_zone(). >>>> >>>> We also cannot determine nid from walking through memblocks after >>>> remove_memory_block_devices() is called. >>>> >>>> Therefore, pass nid down from the beginning of hotremove to where >>>> it is used for the accounting purposes. >>> >>> I was happy to finally remove that nid parameter for good in: >>> >>> commit 65a2aa5f482ed0c1b5afb9e6b0b9e0b16bb8b616 >>> Author: David Hildenbrand >>> Date: Tue Sep 7 19:55:04 2021 -0700 >>> >>> mm/memory_hotplug: remove nid parameter from arch_remove_memory() >>> >>> To ask the real question: Do we really need this counter per-nid at all? >>> >>> Seems to over-complicate things. >> >> Case in point: I think the handling is wrong? >> >> Just because some memory belongs to a nid doesn't mean that the vmemmap >> was allocated from that nid? > > I believe when we hot-add we use nid for the memory that is being > added to account vmemmap, and when we do hot-remove we also use nid of > the memory that is being removed. But, you are correct, this does not > guarantee that the actual vmemmap memory is being allocated or removed > from the given nid. Right. For boot memory that we might want to unplug later it might be different. I recall that with "movable_node", we might end up allocating the vmemmap from remote nodes, such that all memory of a node stays movable. That's why __earlyonly_bootmem_alloc() ends up calling memblock_alloc_try_nid_raw(), to fallback to other nodes if required. > >> Wouldn't we want to look at the actual nid the vmemmap page belongs to >> that we are removing? > > I am now looking into converting this counter to be system wide, i.e. > vm_event, it is all done under hotplug lock, so there is no > contention. That would be easiest, assuming per-node information is not strictly required for now. -- Cheers, David / dhildenb