Right, the only cgroup that does is cpusets because it binds the memory
allocations to a set of nodes.
__GFP_HARDWALL doesn't mean that the allocation won't be constrained, this
is a common misconception. __GFP_HARDWALL only prevents us from looking
at our cpuset.mem_exclusive flag and checking our nearest common ancestor
cpuset if we can block.
The cpusets case is actually the easiest to fix: use GFP_ATOMIC.
GFP_ATOMIC allocations aren't bound by any cpuset and, in the general
case, can allocate below the min watermark because of
ALLOC_HARD | ALLOC_HARDER in the page allocator which creates the notion
of "memory reserves" available to these tasks. Then, success really
depends on the setting of the watermarks instead.
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