f2fs: write checkpoint during FG_GC

If there's not enough free sections each of which consistis of large segments,
we can hit no free section for upcoming section allocation. Let's reclaim some
prefree segments by writing checkpoints.
Signed-off-by: Byungki Lee <dominicus79@gmail.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/gc.c

@@ -1790,23 +1790,31 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
 	if (sync)
 		goto stop;
 
-	if (has_not_enough_free_secs(sbi, sec_freed, 0)) {
-		if (skipped_round <= MAX_SKIP_GC_COUNT ||
-					skipped_round * 2 < round) {
-			segno = NULL_SEGNO;
-			goto gc_more;
-		}
+	if (!has_not_enough_free_secs(sbi, sec_freed, 0))
+		goto stop;
 
-		if (first_skipped < last_skipped &&
-				(last_skipped - first_skipped) >
-						sbi->skipped_gc_rwsem) {
-			f2fs_drop_inmem_pages_all(sbi, true);
-			segno = NULL_SEGNO;
-			goto gc_more;
-		}
-		if (gc_type == FG_GC && !is_sbi_flag_set(sbi, SBI_CP_DISABLED))
+	if (skipped_round <= MAX_SKIP_GC_COUNT || skipped_round * 2 < round) {
+
+		/* Write checkpoint to reclaim prefree segments */
+		if (free_sections(sbi) < NR_CURSEG_PERSIST_TYPE &&
+				prefree_segments(sbi) &&
+				!is_sbi_flag_set(sbi, SBI_CP_DISABLED)) {
 			ret = f2fs_write_checkpoint(sbi, &cpc);
-	}
+			if (ret)
+				goto stop;
+		}
+		segno = NULL_SEGNO;
+		goto gc_more;
+	}
+	if (first_skipped < last_skipped &&
+			(last_skipped - first_skipped) >
+					sbi->skipped_gc_rwsem) {
+		f2fs_drop_inmem_pages_all(sbi, true);
+		segno = NULL_SEGNO;
+		goto gc_more;
+	}
+	if (gc_type == FG_GC && !is_sbi_flag_set(sbi, SBI_CP_DISABLED))
+		ret = f2fs_write_checkpoint(sbi, &cpc);
 stop:
 	SIT_I(sbi)->last_victim[ALLOC_NEXT] = 0;
 	SIT_I(sbi)->last_victim[FLUSH_DEVICE] = init_segno;