On 10.09.20 14:36, Laurent Dufour wrote: > 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@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(). > > 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. > That would have been my suggestion to definitely fix it - maybe Michal/Oscar have a better suggestion know that we know what's going on. -- Thanks, David / dhildenb
