Messages in this thread | | | Subject | Re: [PATCH] mm: don't rely on system state to detect hot-plug operations | From | Laurent Dufour <> | Date | Thu, 10 Sep 2020 14:36:13 +0200 |
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Le 10/09/2020 à 14:00, David Hildenbrand a écrit : > On 10.09.20 13:35, Laurent Dufour wrote: >> Le 10/09/2020 à 13:12, Michal Hocko a écrit : >>> On Thu 10-09-20 09:51:39, Laurent Dufour wrote: >>>> Le 10/09/2020 à 09:23, Michal Hocko a écrit : >>>>> On Wed 09-09-20 18:07:15, Laurent Dufour wrote: >>>>>> Le 09/09/2020 à 12:59, Michal Hocko a écrit : >>>>>>> On Wed 09-09-20 11:21:58, Laurent Dufour wrote: >>>>> [...] >>>>>>>> For the point a, using the enum allows to know in >>>>>>>> register_mem_sect_under_node() if the link operation is due to a hotplug >>>>>>>> operation or done at boot time. >>>>>>> >>>>>>> Yes, but let me repeat. We have a mess here and different paths check >>>>>>> for the very same condition by different ways. We need to unify those. >>>>>> >>>>>> What are you suggesting to unify these checks (using a MP_* enum as >>>>>> suggested by David, something else)? >>>>> >>>>> We do have system_state check spread at different places. I would use >>>>> this one and wrap it behind a helper. Or have I missed any reason why >>>>> that wouldn't work for this case? >>>> >>>> That would not work in that case because memory can be hot-added at the >>>> SYSTEM_SCHEDULING system state and the regular memory is also registered at >>>> that system state too. So system state is not enough to discriminate between >>>> the both. >>> >>> If that is really the case all other places need a fix as well. >>> Btw. could you be more specific about memory hotplug during early boot? >>> How that happens? I am only aware of https://lkml.kernel.org/r/20200818110046.6664-1-osalvador@suse.de >>> and that doesn't happen as early as SYSTEM_SCHEDULING. >> >> That points has been raised by David, quoting him here: >> >>> IIRC, ACPI can hotadd memory while SCHEDULING, this patch would break that. >>> >>> Ccing Oscar, I think he mentioned recently that this is the case with ACPI. >> >> Oscar told that he need to investigate further on that. >> >> On my side I can't get these ACPI "early" hot-plug operations to happen so I >> can't check that. >> >> If this is clear that ACPI memory hotplug doesn't happen at SYSTEM_SCHEDULING, >> the patch I proposed at first is enough to fix the issue. >> > > Booting a qemu guest with 4 coldplugged DIMMs gives me: > > :/root# dmesg | grep link_mem > [ 0.302247] link_mem_sections() during 1 > [ 0.445086] link_mem_sections() during 1 > [ 0.445766] link_mem_sections() during 1 > [ 0.446749] link_mem_sections() during 1 > [ 0.447746] link_mem_sections() during 1 > > So AFAICs everything happens during SYSTEM_SCHEDULING - boot memory and > ACPI (cold)plug. > > To make forward progress with this, relying on the system_state is > obviously not sufficient. > > 1. We have to fix this instance and the instance directly in > get_nid_for_pfn() by passing in the context (I once had a patch to clean > that up, to not have two state checks, but it got lost somewhere). > > 2. The "system_state < SYSTEM_RUNNING" check in > register_memory_resource() is correct. Actual memory hotplug after boot > is not impacted. (I remember we discussed this exact behavior back then) > > 3. build_all_zonelists() should work as expected, called from > start_kernel() before sched_init().
I'm bit confused now. Since hotplug operation is happening at SYSTEM_SCHEDULING like the regular memory registration, would it be enough to add a parameter to register_mem_sect_under_node() (reworking the memmap_context enum)? That way the check is not based on the system state but on the calling path.
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