mm, hugetlb: don't require CMA for runtime gigantic pages

mm, hugetlb: don't require CMA for runtime gigantic pages

Commit 944d9fec8d7a ("hugetlb: add support for gigantic page allocation
at runtime") has added the runtime gigantic page allocation via
alloc_contig_range(), making this support available only when CONFIG_CMA
is enabled.  Because it doesn't depend on MIGRATE_CMA pageblocks and the
associated infrastructure, it is possible with few simple adjustments to
require only CONFIG_MEMORY_ISOLATION instead of full CONFIG_CMA.

After this patch, alloc_contig_range() and related functions are
available and used for gigantic pages with just CONFIG_MEMORY_ISOLATION
enabled.  Note CONFIG_CMA selects CONFIG_MEMORY_ISOLATION.  This allows
supporting runtime gigantic pages without the CMA-specific checks in
page allocator fastpaths.

Signed-off-by: Vlastimil Babka <[email protected]>
Cc: Luiz Capitulino <[email protected]>
Cc: Kirill A. Shutemov <[email protected]>
Cc: Zhang Yanfei <[email protected]>
Cc: Yasuaki Ishimatsu <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Hillf Danton <[email protected]>
Cc: Mike Kravetz <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>