Add a configure option to group pages by mobility

The grouping mechanism has some memory overhead and a more complex allocation
path.  This patch allows the strategy to be disabled for small memory systems
or if it is known the workload is suffering because of the strategy.  It also
acts to show where the page groupings strategy interacts with the standard
buddy allocator.

Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Joel Schopp <jschopp@austin.ibm.com>
Cc: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 13 insertions, 0 deletions

diff --git a/init/Kconfig b/init/Kconfig
index 54f31a191b88..bab643f7717f 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -607,6 +607,19 @@ config BASE_SMALL
         default 0 if BASE_FULL
         default 1 if !BASE_FULL
 
+config PAGE_GROUP_BY_MOBILITY
+        bool "Group pages based on their mobility in the page allocator"
+        def_bool y
+        help
+          The standard allocator will fragment memory over time which means
+          that high order allocations will fail even if kswapd is running. If
+          this option is set, the allocator will try and group page types
+          based on their ability to migrate or reclaim. This is a best effort
+          attempt at lowering fragmentation which a few workloads care about.
+          The loss is a more complex allocator that may perform slower. If
+          you are interested in working with large pages, say Y and set
+          /proc/sys/vm/min_free_bytes to 16374. Otherwise say N
+
 menuconfig MODULES
         bool "Enable loadable module support"
         help