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[2003:cb:c731:3d00:918f:ce94:4280:80f0]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-35e537da921sm5302957f8f.17.2024.06.03.13.53.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 03 Jun 2024 13:53:04 -0700 (PDT) Message-ID: Date: Mon, 3 Jun 2024 22:53:03 +0200 Precedence: bulk X-Mailing-List: linux-cxl@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 8/8] HACK: mm: memory_hotplug: Drop memblock_phys_free() call in try_remove_memory() To: Mike Rapoport Cc: Jonathan Cameron , Dan Williams , linux-cxl@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Sudeep Holla , Andrew Morton , Will Deacon , Jia He , Mike Rapoport , linuxarm@huawei.com, catalin.marinas@arm.com, Anshuman.Khandual@arm.com, Yuquan Wang , Oscar Salvador , Lorenzo Pieralisi , James Morse References: <20240529171236.32002-1-Jonathan.Cameron@huawei.com> <20240529171236.32002-9-Jonathan.Cameron@huawei.com> <92ea53c6-a93b-4ab8-8aec-7f88300576eb@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 03.06.24 12:43, Mike Rapoport wrote: > On Mon, Jun 03, 2024 at 11:14:00AM +0200, David Hildenbrand wrote: >> On 03.06.24 09:57, Mike Rapoport wrote: >>> On Fri, May 31, 2024 at 09:49:32AM +0200, David Hildenbrand wrote: >>>> On 29.05.24 19:12, Jonathan Cameron wrote: >>>>> I'm not sure what this is balancing, but it if is necessary then the reserved >>>>> memblock approach can't be used to stash NUMA node assignments as after the >>>>> first add / remove cycle the entry is dropped so not available if memory is >>>>> re-added at the same HPA. >>>>> >>>>> This patch is here to hopefully spur comments on what this is there for! >>>>> >>>>> Signed-off-by: Jonathan Cameron >>>>> --- >>>>> mm/memory_hotplug.c | 2 +- >>>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>>> >>>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >>>>> index 431b1f6753c0..3d8dd4749dfc 100644 >>>>> --- a/mm/memory_hotplug.c >>>>> +++ b/mm/memory_hotplug.c >>>>> @@ -2284,7 +2284,7 @@ static int __ref try_remove_memory(u64 start, u64 size) >>>>> } >>>>> if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK)) { >>>>> - memblock_phys_free(start, size); >>>>> + // memblock_phys_free(start, size); >>>>> memblock_remove(start, size); >>>>> } >>>> >>>> memblock_phys_free() works on memblock.reserved, memblock_remove() works on >>>> memblock.memory. >>>> >>>> If you take a look at the doc at the top of memblock.c: >>>> >>>> memblock.memory: physical memory available to the system >>>> memblock.reserved: regions that were allocated [during boot] >>>> >>>> >>>> memblock.memory is supposed to be a superset of memblock.reserved. Your >>> >>> No it's not. >>> memblock.reserved is more of "if there is memory, don't touch it". >> >> Then we should certainly clarify that in the comments! :P > > You are welcome to send a patch :-P I'll try once I understood what changed ever since you documented that in 2018 -- or if we missed that detail back then already. > >> But for the memory hotunplug case, that's most likely why that code was >> added. And it only deals with ordinary system RAM, not weird reservations >> you describe below. > > The commit that added memblock_free() at the first place (f9126ab9241f > ("memory-hotplug: fix wrong edge when hot add a new node")) does not really > describe why that was required :( > > But at a quick glance it looks completely spurious. There are more details [1] but I also did not figure out why the memblock_free() was really required to resolve that issue. [1] https://marc.info/?l=linux-kernel&m=142961156129456&w=2 -- Cheers, David / dhildenb