f2fs: fix to correct freed section number during gc

This patch fixes to maintain the right section count freed in garbage
collecting when triggering a foreground gc.

Besides, when a foreground gc is running on current selected section, once
we fail to gc one segment, it's better to abandon gcing the left segments
in current section, because anyway we will select next victim for
foreground gc, so gc on the left segments in previous section will become
overhead and also cause the long latency for caller.
Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/gc.c

@@ -802,7 +802,7 @@ int f2fs_gc(struct f2fs_sb_info *sbi)
 	unsigned int segno = NULL_SEGNO;
 	unsigned int i;
 	int gc_type = BG_GC;
-	int nfree = 0;
+	int sec_freed = 0;
 	int ret = -1;
 	struct cp_control cpc;
 	struct gc_inode_list gc_list = {
@@ -817,7 +817,7 @@ int f2fs_gc(struct f2fs_sb_info *sbi)
 	if (unlikely(f2fs_cp_error(sbi)))
 		goto stop;
 
-	if (gc_type == BG_GC && has_not_enough_free_secs(sbi, nfree)) {
+	if (gc_type == BG_GC && has_not_enough_free_secs(sbi, sec_freed)) {
 		gc_type = FG_GC;
 		if (__get_victim(sbi, &segno, gc_type) || prefree_segments(sbi))
 			write_checkpoint(sbi, &cpc);
@@ -832,13 +832,23 @@ int f2fs_gc(struct f2fs_sb_info *sbi)
 		ra_meta_pages(sbi, GET_SUM_BLOCK(sbi, segno), sbi->segs_per_sec,
 								META_SSA);
 
-	for (i = 0; i < sbi->segs_per_sec; i++)
-		nfree += do_garbage_collect(sbi, segno + i, &gc_list, gc_type);
+	for (i = 0; i < sbi->segs_per_sec; i++) {
+		/*
+		 * for FG_GC case, halt gcing left segments once failed one
+		 * of segments in selected section to avoid long latency.
+		 */
+		if (!do_garbage_collect(sbi, segno + i, &gc_list, gc_type) &&
+				gc_type == FG_GC)
+			break;
+	}
+
+	if (i == sbi->segs_per_sec && gc_type == FG_GC)
+		sec_freed++;
 
 	if (gc_type == FG_GC)
 		sbi->cur_victim_sec = NULL_SEGNO;
 
-	if (has_not_enough_free_secs(sbi, nfree))
+	if (has_not_enough_free_secs(sbi, sec_freed))
 		goto gc_more;
 
 	if (gc_type == FG_GC)