Allow huge page allocations to use GFP_HIGH_MOVABLE

Huge pages are not movable so are not allocated from ZONE_MOVABLE.  However,
as ZONE_MOVABLE will always have pages that can be migrated or reclaimed, it
can be used to satisfy hugepage allocations even when the system has been
running a long time.  This allows an administrator to resize the hugepage pool
at runtime depending on the size of ZONE_MOVABLE.

This patch adds a new sysctl called hugepages_treat_as_movable.  When a
non-zero value is written to it, future allocations for the huge page pool
will use ZONE_MOVABLE.  Despite huge pages being non-movable, we do not
introduce additional external fragmentation of note as huge pages are always
the largest contiguous block we care about.

[akpm@linux-foundation.org: various fixes]
Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 2ce7acf841ae..48dae075d5c2 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -826,6 +826,14 @@ static ctl_table vm_table[] = {
                 .mode           = 0644,
                 .proc_handler   = &proc_dointvec,
          },
+         {
+                .ctl_name       = CTL_UNNUMBERED,
+                .procname       = "hugepages_treat_as_movable",
+                .data           = &hugepages_treat_as_movable,
+                .maxlen         = sizeof(int),
+                .mode           = 0644,
+                .proc_handler   = &hugetlb_treat_movable_handler,
+        },
 #endif
         {
                 .ctl_name       = VM_LOWMEM_RESERVE_RATIO,