mm, compaction: introduce direct compaction priority

In the context of direct compaction, for some types of allocations we
would like the compaction to either succeed or definitely fail while
trying as hard as possible.  Current async/sync_light migration mode is
insufficient, as there are heuristics such as caching scanner positions,
marking pageblocks as unsuitable or deferring compaction for a zone.  At
least the final compaction attempt should be able to override these
heuristics.

To communicate how hard compaction should try, we replace migration mode
with a new enum compact_priority and change the relevant function
signatures.  In compact_zone_order() where struct compact_control is
constructed, the priority is mapped to suitable control flags.  This
patch itself has no functional change, as the current priority levels
are mapped back to the same migration modes as before.  Expanding them
will be done next.

Note that !CONFIG_COMPACTION variant of try_to_compact_pages() is
removed, as the only caller exists under CONFIG_COMPACTION.

Link: http://lkml.kernel.org/r/20160721073614.24395-8-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 6 deletions

diff --git a/mm/compaction.c b/mm/compaction.c
index fee1118c8b94..4719a391242f 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1626,7 +1626,7 @@ out:
 }
 
 static enum compact_result compact_zone_order(struct zone *zone, int order,
-                gfp_t gfp_mask, enum migrate_mode mode, int *contended,
+                gfp_t gfp_mask, enum compact_priority prio, int *contended,
                 unsigned int alloc_flags, int classzone_idx)
 {
         enum compact_result ret;
@@ -1636,7 +1636,8 @@ static enum compact_result compact_zone_order(struct zone *zone, int order,
                 .order = order,
                 .gfp_mask = gfp_mask,
                 .zone = zone,
-                .mode = mode,
+                .mode = (prio == COMPACT_PRIO_ASYNC) ?
+                                        MIGRATE_ASYNC : MIGRATE_SYNC_LIGHT,
                 .alloc_flags = alloc_flags,
                 .classzone_idx = classzone_idx,
                 .direct_compaction = true,
@@ -1669,7 +1670,7 @@ int sysctl_extfrag_threshold = 500;
  */
 enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
                 unsigned int alloc_flags, const struct alloc_context *ac,
-                enum migrate_mode mode, int *contended)
+                enum compact_priority prio, int *contended)
 {
         int may_enter_fs = gfp_mask & __GFP_FS;
         int may_perform_io = gfp_mask & __GFP_IO;
@@ -1684,7 +1685,7 @@ enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
         if (!may_enter_fs || !may_perform_io)
                 return COMPACT_SKIPPED;
 
-        trace_mm_compaction_try_to_compact_pages(order, gfp_mask, mode);
+        trace_mm_compaction_try_to_compact_pages(order, gfp_mask, prio);
 
         /* Compact each zone in the list */
         for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, ac->high_zoneidx,
@@ -1697,7 +1698,7 @@ enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
                         continue;
                 }
 
-                status = compact_zone_order(zone, order, gfp_mask, mode,
+                status = compact_zone_order(zone, order, gfp_mask, prio,
                                 &zone_contended, alloc_flags,
                                 ac_classzone_idx(ac));
                 rc = max(status, rc);
@@ -1731,7 +1732,7 @@ enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
                         goto break_loop;
                 }
 
-                if (mode != MIGRATE_ASYNC && (status == COMPACT_COMPLETE ||
+                if (prio != COMPACT_PRIO_ASYNC && (status == COMPACT_COMPLETE ||
                                         status == COMPACT_PARTIAL_SKIPPED)) {
                         /*
                          * We think that allocation won't succeed in this zone