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@xxxxxxx >> 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(). -- Thanks, David / dhildenb
