Re: [PATCH] mm: don't rely on system state to detect hot-plug operations
From: Laurent Dufour
Date: Thu Sep 10 2020 - 17:58:45 EST
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.