mm/compaction: factor out code to test if we should run compaction for target order

We always do zone_watermark_ok check and compaction_suitable check
together to test if compaction for target order should be ran.  Factor
these code out to remove repeat code.

Link: https://lkml.kernel.org/r/20230901155141.249860-7-shikemeng@huaweicloud.comSigned-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/compaction.c

@@ -2378,6 +2378,30 @@ bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
 	return false;
 }
 
+/*
+ * Should we do compaction for target allocation order.
+ * Return COMPACT_SUCCESS if allocation for target order can be already
+ * satisfied
+ * Return COMPACT_SKIPPED if compaction for target order is likely to fail
+ * Return COMPACT_CONTINUE if compaction for target order should be ran
+ */
+static enum compact_result
+compaction_suit_allocation_order(struct zone *zone, unsigned int order,
+				 int highest_zoneidx, unsigned int alloc_flags)
+{
+	unsigned long watermark;
+
+	watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
+	if (zone_watermark_ok(zone, order, watermark, highest_zoneidx,
+			      alloc_flags))
+		return COMPACT_SUCCESS;
+
+	if (!compaction_suitable(zone, order, highest_zoneidx))
+		return COMPACT_SKIPPED;
+
+	return COMPACT_CONTINUE;
+}
+
 static enum compact_result
 compact_zone(struct compact_control *cc, struct capture_control *capc)
 {
@@ -2403,19 +2427,11 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
 	cc->migratetype = gfp_migratetype(cc->gfp_mask);
 
 	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;
-
-		/* Compaction is likely to fail */
-		if (!compaction_suitable(cc->zone, cc->order,
-					 cc->highest_zoneidx))
-			return COMPACT_SKIPPED;
+		ret = compaction_suit_allocation_order(cc->zone, cc->order,
+						       cc->highest_zoneidx,
+						       cc->alloc_flags);
+		if (ret != COMPACT_CONTINUE)
+			return ret;
 	}
 
 	/*
@@ -2914,6 +2930,7 @@ static bool kcompactd_node_suitable(pg_data_t *pgdat)
 	int zoneid;
 	struct zone *zone;
 	enum zone_type highest_zoneidx = pgdat->kcompactd_highest_zoneidx;
+	enum compact_result ret;
 
 	for (zoneid = 0; zoneid <= highest_zoneidx; zoneid++) {
 		zone = &pgdat->node_zones[zoneid];
@@ -2921,14 +2938,10 @@ static bool kcompactd_node_suitable(pg_data_t *pgdat)
 		if (!populated_zone(zone))
 			continue;
 
-		/* 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))
+		ret = compaction_suit_allocation_order(zone,
+				pgdat->kcompactd_max_order,
+				highest_zoneidx, ALLOC_WMARK_MIN);
+		if (ret == COMPACT_CONTINUE)
 			return true;
 	}
 
@@ -2951,6 +2964,8 @@ static void kcompactd_do_work(pg_data_t *pgdat)
 		.ignore_skip_hint = false,
 		.gfp_mask = GFP_KERNEL,
 	};
+	enum compact_result ret;
+
 	trace_mm_compaction_kcompactd_wake(pgdat->node_id, cc.order,
 							cc.highest_zoneidx);
 	count_compact_event(KCOMPACTD_WAKE);
@@ -2965,12 +2980,9 @@ static void kcompactd_do_work(pg_data_t *pgdat)
 		if (compaction_deferred(zone, cc.order))
 			continue;
 
-		/* 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))
+		ret = compaction_suit_allocation_order(zone,
+				cc.order, zoneid, ALLOC_WMARK_MIN);
+		if (ret != COMPACT_CONTINUE)
 			continue;
 
 		if (kthread_should_stop())