[RFC 0/3] extend vmalloc support for constrained allocations

[Michal Hocko]

Hi,
based on a recent discussion with Dave and Neil [1] I have tried to
implement NOFS, NOIO, NOFAIL support for the vmalloc to make
life of kvmalloc users easier.

A requirement for NOFAIL support for kvmalloc was new to me but this
seems to be really needed by the xfs code.

NOFS/NOIO was a known and a long term problem which was hoped to be
handled by the scope API. Those scope should have been used at the
reclaim recursion boundaries both to document them and also to remove
the necessity of NOFS/NOIO constrains for all allocations within that
scope. Instead workarounds were developed to wrap a single allocation
instead (like ceph_kvmalloc).

First patch implements NOFS/NOIO support for vmalloc. The second one
adds NOFAIL support and the third one bundles all together into kvmalloc
and drops ceph_kvmalloc which can use kvmalloc directly now.

Please note that this is RFC and I haven't done any testing on this yet.
I hope I haven't missed anything in the vmalloc allocator. It would be
really great if Christoph and Uladzislau could have a look.

Thanks!

[1] http://lkml.kernel.org/r/163184741778.29351.16920832234899124642.stgit@noble.brown