mm: allow CONFIG_MIGRATION to be set without CONFIG_NUMA or memory hot-remove

CONFIG_MIGRATION currently depends on CONFIG_NUMA or on the architecture
being able to hot-remove memory.  The main users of page migration such as
sys_move_pages(), sys_migrate_pages() and cpuset process migration are
only beneficial on NUMA so it makes sense.

As memory compaction will operate within a zone and is useful on both NUMA
and non-NUMA systems, this patch allows CONFIG_MIGRATION to be set if the
user selects CONFIG_COMPACTION as an option.

[akpm@linux-foundation.org: Depend on CONFIG_HUGETLB_PAGE]
Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Reviewed-by: Christoph Lameter <cl@linux-foundation.org>
Reviewed-by: Rik van Riel <riel@redhat.com>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 14 insertions, 3 deletions

diff --git a/mm/Kconfig b/mm/Kconfig
index 9c61158308d..527136b2238 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -172,6 +172,15 @@ config SPLIT_PTLOCK_CPUS
         default "4"
 
 #
+# support for memory compaction
+config COMPACTION
+        bool "Allow for memory compaction"
+        select MIGRATION
+        depends on EXPERIMENTAL && HUGETLB_PAGE && MMU
+        help
+          Allows the compaction of memory for the allocation of huge pages.
+
+#
 # support for page migration
 #
 config MIGRATION
@@ -180,9 +189,11 @@ config MIGRATION
         depends on NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE
         help
           Allows the migration of the physical location of pages of processes
-          while the virtual addresses are not changed. This is useful for
-          example on NUMA systems to put pages nearer to the processors accessing
-          the page.
+          while the virtual addresses are not changed. This is useful in
+          two situations. The first is on NUMA systems to put pages nearer
+          to the processors accessing. The second is when allocating huge
+          pages as migration can relocate pages to satisfy a huge page
+          allocation instead of reclaiming.
 
 config PHYS_ADDR_T_64BIT
         def_bool 64BIT || ARCH_PHYS_ADDR_T_64BIT