mm/compaction: make defer_compaction and compaction_deferred static

defer_compaction() and compaction_deferred() and compaction_restarting()
in mm/compaction.c won't be used in other files, so make them static, and
remove the declaration in the header file.

Take the chance to fix a typo.

Link: https://lkml.kernel.org/r/20201123170801.GA9625@rlkSigned-off-by: Hui Su <sh_def@163.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Nitin Gupta <nigupta@nvidia.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Mateusz Nosek <mateusznosek0@gmail.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/compaction.h

@@ -98,11 +98,8 @@ extern void reset_isolation_suitable(pg_data_t *pgdat);
 extern enum compact_result compaction_suitable(struct zone *zone, int order,
 		unsigned int alloc_flags, int highest_zoneidx);
 
-extern void defer_compaction(struct zone *zone, int order);
-extern bool compaction_deferred(struct zone *zone, int order);
 extern void compaction_defer_reset(struct zone *zone, int order,
 				bool alloc_success);
-extern bool compaction_restarting(struct zone *zone, int order);
 
 /* Compaction has made some progress and retrying makes sense */
 static inline bool compaction_made_progress(enum compact_result result)
@@ -194,15 +191,6 @@ static inline enum compact_result compaction_suitable(struct zone *zone, int ord
 	return COMPACT_SKIPPED;
 }
 
-static inline void defer_compaction(struct zone *zone, int order)
-{
-}
-
-static inline bool compaction_deferred(struct zone *zone, int order)
-{
-	return true;
-}
-
 static inline bool compaction_made_progress(enum compact_result result)
 {
 	return false;

mm/compaction.c

@@ -157,7 +157,7 @@ EXPORT_SYMBOL(__ClearPageMovable);
  * allocation success. 1 << compact_defer_shift, compactions are skipped up
  * to a limit of 1 << COMPACT_MAX_DEFER_SHIFT
  */
-void defer_compaction(struct zone *zone, int order)
+static void defer_compaction(struct zone *zone, int order)
 {
 	zone->compact_considered = 0;
 	zone->compact_defer_shift++;
@@ -172,7 +172,7 @@ void defer_compaction(struct zone *zone, int order)
 }
 
 /* Returns true if compaction should be skipped this time */
-bool compaction_deferred(struct zone *zone, int order)
+static bool compaction_deferred(struct zone *zone, int order)
 {
 	unsigned long defer_limit = 1UL << zone->compact_defer_shift;
 
@@ -209,7 +209,7 @@ void compaction_defer_reset(struct zone *zone, int order,
 }
 
 /* Returns true if restarting compaction after many failures */
-bool compaction_restarting(struct zone *zone, int order)
+static bool compaction_restarting(struct zone *zone, int order)
 {
 	if (order < zone->compact_order_failed)
 		return false;
@@ -237,7 +237,7 @@ static void reset_cached_positions(struct zone *zone)
 }
 
 /*
- * Compound pages of >= pageblock_order should consistenly be skipped until
+ * Compound pages of >= pageblock_order should consistently be skipped until
  * released. It is always pointless to compact pages of such order (if they are
  * migratable), and the pageblocks they occupy cannot contain any free pages.
  */