On Thu 10-09-20 13:35:32, 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. : Please, note that upstream has fixed that differently (and unintentionally) by : adding another boot state (SYSTEM_SCHEDULING), which is set before smp_init(). : That should happen before memory hotplug events even with memhp_default_state=online. : Backporting that would be too intrusive. Either I am confused or the above says that no hotplug should happen during SYSTEM_SCHEDULING even in the above case. I really have hard time to imagine how an early boot hotplug should even work. We start with a memory layout provided by a BIOS/FW and intiailize it statically. How would a hotplug even actually trigger that early? -- Michal Hocko SUSE Labs
