mm: disable DEFERRED_STRUCT_PAGE_INIT on !NO_BOOTMEM

When we have !NO_BOOTMEM, the deferred page struct initialization
doesn't work well because the pages reserved in bootmem are released to
the page allocator uncoditionally.  It causes memory corruption and
system crash eventually.

As Mel suggested, the bootmem is retiring slowly.  We fix the issue by
simply hiding DEFERRED_STRUCT_PAGE_INIT when bootmem is enabled.

Link: http://lkml.kernel.org/r/1460602170-5821-1-git-send-email-gwshan@linux.vnet.ibm.com
Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/Kconfig

@@ -648,7 +648,7 @@ config DEFERRED_STRUCT_PAGE_INIT
 	bool "Defer initialisation of struct pages to kthreads"
 	default n
 	depends on ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
-	depends on MEMORY_HOTPLUG
+	depends on NO_BOOTMEM && MEMORY_HOTPLUG
 	depends on !FLATMEM
 	help
 	  Ordinarily all struct pages are initialised during early boot in a