Re: [PATCH] mm/compaction: introduce a helper compact_zone_counters_init()

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 23 Jul 2019 10:12:18 +0200 Michal Hocko <mhocko@suse.com> wrote:

> On Tue 23-07-19 04:08:15, Yafang Shao wrote:
> > This is the follow-up of the
> > commit "mm/compaction.c: clear total_{migrate,free}_scanned before scanning a new zone".
> > 
> > These counters are used to track activities during compacting a zone,
> > and they will be set to zero before compacting a new zone in all compact
> > paths. Move all these common settings into compact_zone() for better
> > management. A new helper compact_zone_counters_init() is introduced for
> > this purpose.
> 
> The helper seems excessive a bit because we have a single call site but
> other than that this is an improvement to the current fragile and
> duplicated code.
> 
> I would just get rid of the helper and squash it to your previous patch
> which Andrew already took to the mm tree.

--- a/mm/compaction.c~mm-compaction-clear-total_migratefree_scanned-before-scanning-a-new-zone-fix-fix
+++ a/mm/compaction.c
@@ -2068,19 +2068,6 @@ bool compaction_zonelist_suitable(struct
 	return false;
 }
 
-
-/*
- * Bellow counters are used to track activities during compacting a zone.
- * Before compacting a new zone, we should init these counters first.
- */
-static void compact_zone_counters_init(struct compact_control *cc)
-{
-	cc->total_migrate_scanned = 0;
-	cc->total_free_scanned = 0;
-	cc->nr_migratepages = 0;
-	cc->nr_freepages = 0;
-}
-
 static enum compact_result
 compact_zone(struct compact_control *cc, struct capture_control *capc)
 {
@@ -2091,7 +2078,15 @@ compact_zone(struct compact_control *cc,
 	const bool sync = cc->mode != MIGRATE_ASYNC;
 	bool update_cached;
 
-	compact_zone_counters_init(cc);
+	/*
+	 * These counters track activities during zone compaction.  Initialize
+	 * them before compacting a new zone.
+	 */
+	cc->total_migrate_scanned = 0;
+	cc->total_free_scanned = 0;
+	cc->nr_migratepages = 0;
+	cc->nr_freepages = 0;
+
 	cc->migratetype = gfpflags_to_migratetype(cc->gfp_mask);
 	ret = compaction_suitable(cc->zone, cc->order, cc->alloc_flags,
 							cc->classzone_idx);
_