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[2003:cb:c73a:3a00:a025:9b06:549e:c16b]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-35dd04c0d3csm10992170f8f.19.2024.06.04.02.39.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 04 Jun 2024 02:39:29 -0700 (PDT) Message-ID: <900bd9b6-a788-4c71-9b43-aff4855ba234@redhat.com> Date: Tue, 4 Jun 2024 11:39:27 +0200 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="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 04.06.24 11:35, Mike Rapoport wrote: > On Mon, Jun 03, 2024 at 10:53:03PM +0200, David Hildenbrand wrote: >> 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 > > The tinkering with memblock there and in f9126ab9241f seem bogus in the > context of memory hotplug on x86. > > I believe that dropping that memblock_phys_free() is right thing to do > regardless of this series. There's no corresponding memblock_alloc() and it > was added as part of a fix for hotunplug on x86 that anyway had memblock > discarded at that point. So when we re-add that memory, we might have still ranges as "reserved". It does sound weird, but you're the boss :) -- Cheers, David / dhildenb _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel