f2fs: refactor f2fs_gc to call checkpoint in urgent condition

The major change is to call checkpoint, if there's not enough space while having
some prefree segments in FG_GC case.

Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/gc.c

@@ -1829,7 +1829,10 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
 		goto stop;
 	}
 
-	if (gc_type == BG_GC && has_not_enough_free_secs(sbi, 0, 0)) {
+	/* Let's run FG_GC, if we don't have enough space. */
+	if (has_not_enough_free_secs(sbi, 0, 0)) {
+		gc_type = FG_GC;
+
 		/*
 		 * For example, if there are many prefree_segments below given
 		 * threshold, we can make them free by checkpoint. Then, we
@@ -1840,8 +1843,6 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
 			if (ret)
 				goto stop;
 		}
-		if (has_not_enough_free_secs(sbi, 0, 0))
-			gc_type = FG_GC;
 	}
 
 	/* f2fs_balance_fs doesn't need to do BG_GC in critical path. */
@@ -1868,19 +1869,15 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
 	if (seg_freed == f2fs_usable_segs_in_sec(sbi, segno))
 		sec_freed++;
 
-	if (gc_type == FG_GC)
+	if (gc_type == FG_GC) {
 		sbi->cur_victim_sec = NULL_SEGNO;
 
-	if (gc_control->init_gc_type == FG_GC ||
-	    !has_not_enough_free_secs(sbi,
-				(gc_type == FG_GC) ? sec_freed : 0, 0)) {
-		if (gc_type == FG_GC && sec_freed < gc_control->nr_free_secs)
-			goto go_gc_more;
-		goto stop;
-	}
-
-	/* FG_GC stops GC by skip_count */
-	if (gc_type == FG_GC) {
+		if (!has_not_enough_free_secs(sbi, sec_freed, 0)) {
+			if (!gc_control->no_bg_gc &&
+			    sec_freed < gc_control->nr_free_secs)
+				goto go_gc_more;
+			goto stop;
+		}
 		if (sbi->skipped_gc_rwsem)
 			skipped_round++;
 		round++;
@@ -1889,6 +1886,8 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
 			ret = f2fs_write_checkpoint(sbi, &cpc);
 			goto stop;
 		}
+	} else if (!has_not_enough_free_secs(sbi, 0, 0)) {
+		goto stop;
 	}
 
 	__get_secs_required(sbi, NULL, &upper_secs, NULL);