mm, hugepages: add mremap() support for hugepage backed vma

Support mremap() for hugepage backed vma segment by simply repositioning
page table entries.  The page table entries are repositioned to the new
virtual address on mremap().

Hugetlb mremap() support is of course generic; my motivating use case is
a library (hugepage_text), which reloads the ELF text of executables in
hugepages.  This significantly increases the execution performance of
said executables.

Restrict the mremap operation on hugepages to up to the size of the
original mapping as the underlying hugetlb reservation is not yet
capable of handling remapping to a larger size.

During the mremap() operation we detect pmd_share'd mappings and we
unshare those during the mremap().  On access and fault the sharing is
established again.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Mina Almasry <[email protected]>
Reviewed-by: Mike Kravetz <[email protected]>
Cc: Ken Chen <[email protected]>
Cc: Chris Kennelly <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Kirill Shutemov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions