mm: speedup mremap on 1GB or larger regions

Android needs to move large memory regions for garbage collection.  The GC
requires moving physical pages of multi-gigabyte heap using mremap.
During this move, the application threads have to be paused for
correctness.  It is critical to keep this pause as short as possible to
avoid jitters during user interaction.

Optimize mremap for >= 1GB-sized regions by moving at the PUD/PGD level if
the source and destination addresses are PUD-aligned.  For
CONFIG_PGTABLE_LEVELS == 3, moving at the PUD level in effect moves PGD
entries, since the PUD entry is “folded back” onto the PGD entry.  Add
HAVE_MOVE_PUD so that architectures where moving at the PUD level isn't
supported/tested can turn this off by not selecting the config.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Kalesh Singh <[email protected]>
Acked-by: Kirill A. Shutemov <[email protected]>
Reported-by: kernel test robot <[email protected]>
Cc: Aneesh Kumar K.V <[email protected]>
Cc: Anshuman Khandual <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Geffon <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Gavin Shan <[email protected]>
Cc: Hassan Naveed <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jia He <[email protected]>
Cc: John Hubbard <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Krzysztof Kozlowski <[email protected]>
Cc: Lokesh Gidra <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Mina Almasry <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Peter Zijlstra (Intel) <[email protected]>
Cc: Ralph Campbell <[email protected]>
Cc: Ram Pai <[email protected]>
Cc: Sami Tolvanen <[email protected]>
Cc: Sandipan Das <[email protected]>
Cc: SeongJae Park <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Steven Price <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Zi Yan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

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