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    SubjectRe: Regression in 2.6.23-rc2-mm2, mounting cpusets causes a hang
    On Wed, 2007-08-15 at 13:36 -0700, Christoph Lameter wrote:
    > 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.

    Well, OK. But Paul really hates #ifdefs in kernel/cpusets.c. He's
    asked me to remove them before, so I avoided them here. Cpusets really
    should use only nodes with memory--i.e., the N_HIGH_MEMORY state.

    > > 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.

    So far. I'm replacing other usage of node_online_map with the
    N_HIGH_MEMORY mask, as we discussed. I should have that patch ready to
    post tomorrow.

    > > 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.

    But, the mask--the N_HIGH_MEMORY array element, that is--is there for
    both NUMA and !NUMA [== N_NORMAL_MEMORY for !CONFIG_HIGHMEM]. We just
    don't initialize it for the !NUMA case, currently.

    > > 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.

    That's what the patch I posted today [option 2] does--statically
    initializes the N_*_MEMORY and N_CPU masks to indicate that node 0
    exists. Serge and Dhaval have tested it on their platform and it solves
    the cpuset mount problem.


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