mm: compaction: refactor __compaction_suitable()

__compaction_suitable() is supposed to check for available migration
targets.  However, it also checks whether the operation was requested via
/proc/sys/vm/compact_memory, and whether the original allocation request
can already succeed.  These don't apply to all callsites.

Move the checks out to the callers, so that later patches can deal with
them one by one.  No functional change intended.

[hannes@cmpxchg.org: fix comment, per Vlastimil]
  Link: https://lkml.kernel.org/r/20230602144942.GC161817@cmpxchg.org
Link: https://lkml.kernel.org/r/20230519123959.77335-4-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 50 insertions, 29 deletions

diff --git a/mm/compaction.c b/mm/compaction.c
index e23e00bec030..bb9b76244a5d 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -2194,24 +2194,10 @@ static enum compact_result compact_finished(struct compact_control *cc)
 }
 
 static enum compact_result __compaction_suitable(struct zone *zone, int order,
-					unsigned int alloc_flags,
 					int highest_zoneidx,
 					unsigned long wmark_target)
 {
 	unsigned long watermark;
-
-	if (is_via_compact_memory(order))
-		return COMPACT_CONTINUE;
-
-	watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
-	/*
-	 * If watermarks for high-order allocation are already met, there
-	 * should be no need for compaction at all.
-	 */
-	if (zone_watermark_ok(zone, order, watermark, highest_zoneidx,
-								alloc_flags))
-		return COMPACT_SUCCESS;
-
 	/*
 	 * Watermarks for order-0 must be met for compaction to be able to
 	 * isolate free pages for migration targets. This means that the
@@ -2240,17 +2226,15 @@ static enum compact_result __compaction_suitable(struct zone *zone, int order,
  * compaction_suitable: Is this suitable to run compaction on this zone now?
  * Returns
  *   COMPACT_SKIPPED  - If there are too few free pages for compaction
- *   COMPACT_SUCCESS  - If the allocation would succeed without compaction
  *   COMPACT_CONTINUE - If compaction should run now
  */
 enum compact_result compaction_suitable(struct zone *zone, int order,
-					unsigned int alloc_flags,
 					int highest_zoneidx)
 {
 	enum compact_result ret;
 	int fragindex;
 
-	ret = __compaction_suitable(zone, order, alloc_flags, highest_zoneidx,
+	ret = __compaction_suitable(zone, order, highest_zoneidx,
 				    zone_page_state(zone, NR_FREE_PAGES));
 	/*
 	 * fragmentation index determines if allocation failures are due to
@@ -2294,7 +2278,16 @@ bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
 	for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
 				ac->highest_zoneidx, ac->nodemask) {
 		unsigned long available;
-		enum compact_result compact_result;
+		unsigned long watermark;
+
+		if (is_via_compact_memory(order))
+			return true;
+
+		/* Allocation can already succeed, nothing to do */
+		watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
+		if (zone_watermark_ok(zone, order, watermark,
+				      ac->highest_zoneidx, alloc_flags))
+			continue;
 
 		/*
 		 * Do not consider all the reclaimable memory because we do not
@@ -2304,9 +2297,8 @@ bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
 		 */
 		available = zone_reclaimable_pages(zone) / order;
 		available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
-		compact_result = __compaction_suitable(zone, order, alloc_flags,
-				ac->highest_zoneidx, available);
-		if (compact_result == COMPACT_CONTINUE)
+		if (__compaction_suitable(zone, order, ac->highest_zoneidx,
+					  available) == COMPACT_CONTINUE)
 			return true;
 	}
 
@@ -2336,11 +2328,23 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
 	INIT_LIST_HEAD(&cc->migratepages);
 
 	cc->migratetype = gfp_migratetype(cc->gfp_mask);
-	ret = compaction_suitable(cc->zone, cc->order, cc->alloc_flags,
-							cc->highest_zoneidx);
-	/* Compaction is likely to fail */
-	if (ret == COMPACT_SUCCESS || ret == COMPACT_SKIPPED)
-		return ret;
+
+	if (!is_via_compact_memory(cc->order)) {
+		unsigned long watermark;
+
+		/* Allocation can already succeed, nothing to do */
+		watermark = wmark_pages(cc->zone,
+					cc->alloc_flags & ALLOC_WMARK_MASK);
+		if (zone_watermark_ok(cc->zone, cc->order, watermark,
+				      cc->highest_zoneidx, cc->alloc_flags))
+			return COMPACT_SUCCESS;
+
+		ret = compaction_suitable(cc->zone, cc->order,
+					  cc->highest_zoneidx);
+		/* Compaction is likely to fail */
+		if (ret == COMPACT_SKIPPED)
+			return ret;
+	}
 
 	/*
 	 * Clear pageblock skip if there were failures recently and compaction
@@ -2844,7 +2848,16 @@ static bool kcompactd_node_suitable(pg_data_t *pgdat)
 		if (!populated_zone(zone))
 			continue;
 
-		if (compaction_suitable(zone, pgdat->kcompactd_max_order, 0,
+		if (is_via_compact_memory(pgdat->kcompactd_max_order))
+			return true;
+
+		/* Allocation can already succeed, check other zones */
+		if (zone_watermark_ok(zone, pgdat->kcompactd_max_order,
+				      min_wmark_pages(zone),
+				      highest_zoneidx, 0))
+			continue;
+
+		if (compaction_suitable(zone, pgdat->kcompactd_max_order,
 					highest_zoneidx) == COMPACT_CONTINUE)
 			return true;
 	}
@@ -2882,10 +2895,18 @@ static void kcompactd_do_work(pg_data_t *pgdat)
 		if (compaction_deferred(zone, cc.order))
 			continue;
 
-		if (compaction_suitable(zone, cc.order, 0, zoneid) !=
-							COMPACT_CONTINUE)
+		if (is_via_compact_memory(cc.order))
+			goto compact;
+
+		/* Allocation can already succeed, nothing to do */
+		if (zone_watermark_ok(zone, cc.order,
+				      min_wmark_pages(zone), zoneid, 0))
 			continue;
 
+		if (compaction_suitable(zone, cc.order,
+					zoneid) != COMPACT_CONTINUE)
+			continue;
+compact:
 		if (kthread_should_stop())
 			return;