[PATCH 05/14] mm: Allow CONFIG_MIGRATION to be set without CONFIG_NUMA or memory hot-remove

[Mel Gorman <mel@csn.ul.ie>]

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>
---
 mm/Kconfig |   18 +++++++++++++++---
 1 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/mm/Kconfig b/mm/Kconfig
index 9c61158..a275a7d 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -172,6 +172,16 @@ config SPLIT_PTLOCK_CPUS
 	default "4"
 
 #
+# support for memory compaction
+config COMPACTION
+	bool "Allow for memory compaction"
+	def_bool y
+	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 +190,11 @@ 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
-- 
1.6.5

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