Re: Regression in 2.6.23-rc2-mm2, mounting cpusets causes a hang

Christoph Lameter
2007-08-15T20:37:29Z

On Wed, 15 Aug 2007, Lee Schermerhorn wrote:

> > So its always true for node 0. The "bit" is set.
>
> The issue is with the N_*_MEMORY masks. They don't get initialized
> properly because node_set_state() is a no-op if !NUMA. So, where we
> look for intersections with or where we AND with the N_*_MEMORY masks we
> get the empty set.

That is intentional. Memory is always present if you are on !NUMA. You can
simply use a default nodemask where only node 0 is set. That is what the
fallback provides. Maybe it does not provide the right thing for cpusets?

> > We are trying to get cpusets to work with !NUMA?
>
> Well, yes. In Serge's case, he's trying to use cpusets with !NUMA.
> He'll have to comment on the reasons for that. Looking at all of the
> #ifdefs and init/Kconfig, CPUSET does not depend on NUMA--only SMP and
> CONTAINERS [altho' methinks CPUSET should select CONTAINERS rather than
> depend on it...]. So, you can use cpusets to partition of cpus in
> non-NUMA configs.

Looks like we need to fix cpuset nodemasks for the !NUMA case then?
It cannot expect to find valid nodemasks if !NUMA.

> In the more general case, tho', I'm looking at all uses of the
> node_online_map and for_each_online_node, for instances where they
> should be replaced with one of the *_MEMORY masks. IMO, generic code
> that is compiled independent of any CONFIG option, like NUMA, should
> just work, independent of the config. Currently, as Serge has shown,

AFAIK this works except for cpusets.

> this is not the case. So, I think we should fix the *_MEMORY maps to be
> correctly populated in both the NUMA and !NUMA cases. A couple of
> options:

There is no point in having a variable if you know the results because of
!NUMA. That is the way nodemask.h has always operated.

> Thoughts?

Lets get either rid of the definitions for the nodemasks in the !NUMA
case or fix their contents to have the right constant value expected in
cpusets.