[PATCH 0/3] hugetlb: V2 constrain allocation/free based on task mempolicy

[Lee Schermerhorn <lee.schermerhorn@hp.com>]

PATCH 0/3 hugetlb: constrain allocation/free based on task mempolicy

Against:  25jun09 mmotm atop the "hugetlb:  balance freeing..."
series

This is V2 of a series of patches to constrain the allocation and
freeing of persistent huge pages using the task NUMA mempolicy of
the task modifying "nr_hugepages".  This series is based on Mel
Gorman's suggestion to use task mempolicy.

V2 addresses review comments from Mel Gorman and Andrew Morton.
See the patch description of patch 2/3.

I have some concerns about a subtle change in behavior [see patch
2/3 and the updated documentation] and the fact that
this mechanism ignores some of the semantics of the mempolicy
mode [again, see the doc].   However, this method seems to work
fairly well.  And, IMO, the resulting code doesn't look all that
bad.

A couple of limitations in this version:

1) I haven't implemented a boot time parameter to constrain the
   boot time allocation of huge pages.  This can be added if
   anyone feels strongly that it is required.

2) I have not implemented a per node nr_overcommit_hugepages as
   David Rientjes and I discussed earlier.  Again, this can be
   added and specific nodes can be addressed using the mempolicy
   as this series does for allocation and free.  However, after
   some experience with the libhugetlbfs test suite, specifically
   attempting to run the test suite constrained by mempolicy and
   a cpuset, I'm thinking that per node overcommit limits might
   not be such a good idea.  This would require an application
   [or the library] to sum the per node limits over the allowed
   nodes and possibly compare to global limits to determine the
   available resources.  Per cpuset limits might work better.
   This are requires more investigation, but this patch series
   doesn't seem to make things worse than they already are in
   this regard.