f2fs: readahead contiguous SSA blocks for f2fs_gc

If there are multi segments in one section, we will read those SSA blocks which
have contiguous address one by one in f2fs_gc. It may lost performance, let's
read ahead SSA blocks by merge multi read request.

Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

fs/f2fs/checkpoint.c

@@ -82,6 +82,7 @@ inline int get_max_meta_blks(struct f2fs_sb_info *sbi, int type)
 		return NM_I(sbi)->max_nid / NAT_ENTRY_PER_BLOCK;
 	case META_SIT:
 		return SIT_BLK_CNT(sbi);
+	case META_SSA:
 	case META_CP:
 		return 0;
 	default:
@@ -90,7 +91,7 @@ inline int get_max_meta_blks(struct f2fs_sb_info *sbi, int type)
 }
 
 /*
- * Readahead CP/NAT/SIT pages
+ * Readahead CP/NAT/SIT/SSA pages
  */
 int ra_meta_pages(struct f2fs_sb_info *sbi, int start, int nrpages, int type)
 {
@@ -125,8 +126,9 @@ int ra_meta_pages(struct f2fs_sb_info *sbi, int start, int nrpages, int type)
 				goto out;
 			prev_blk_addr = blk_addr;
 			break;
+		case META_SSA:
 		case META_CP:
-			/* get cp block addr */
+			/* get ssa/cp block addr */
 			blk_addr = blkno;
 			break;
 		default:

fs/f2fs/f2fs.h

@@ -89,12 +89,13 @@ enum {
 };
 
 /*
- * For CP/NAT/SIT readahead
+ * For CP/NAT/SIT/SSA readahead
  */
 enum {
 	META_CP,
 	META_NAT,
-	META_SIT
+	META_SIT,
+	META_SSA
 };
 
 /* for the list of orphan inodes */

fs/f2fs/gc.c

@@ -708,6 +708,11 @@ gc_more:
 		goto stop;
 	ret = 0;
 
+	/* readahead multi ssa blocks those have contiguous address */
+	if (sbi->segs_per_sec > 1)
+		ra_meta_pages(sbi, GET_SUM_BLOCK(sbi, segno), sbi->segs_per_sec,
+								META_SSA);
+
 	for (i = 0; i < sbi->segs_per_sec; i++)
 		do_garbage_collect(sbi, segno + i, &ilist, gc_type);