[PATCH 0/6] hugetlb: Remove is_file_hugepages() macro

[Adam Litke <agl@us.ibm.com>]

The kernel code is currently peppered with special casing for hugetlbfs
mappings.  In many places we check a struct file's f_op member to see if it
points to the hugetlbfs file_operations in which case we'll employ some sort of
workaround.  The need to check file_operations in this manner suggests that we
are either missing f_op operations, or have deficient abstraction elsewhere.

I am motivated to clean this up for two reasons:  1) The community has asked
for huge pages to be kept "on the side" of the main VM.  I believe these
patches advance that goal.  2) Proper abstraction of hugetlbfs allows the
underlying implementation to be changed without disturbing the main VM.

Removing the is_file_hugepages() macro involved finding all the call sites,
determining the actual incompatibility that huge page mappings introduce, and
applying a relatively trivial fix for the problem.  The following patches
perform this surgery.

When converting these, I have tried to use as general of a solution as
possible.  Review of some of the design decisions would be appreciated --
specifically the use of backing_dev_info for the note about special accounting,
and hugetlbfs sharing the inode_info struct with shmem.

Thanks to Andy Whitcroft and others for review of the preliminary patches.

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