f2fs: return fs_trim if there is no candidate

If there is no candidate to submit discard command during f2fs_trim_fs, let's
return without checkpoint.
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/checkpoint.c

@@ -1249,6 +1249,11 @@ int write_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
 
 	/* this is the case of multiple fstrims without any changes */
 	if (cpc->reason == CP_DISCARD) {
+		if (!exist_trim_candidates(sbi, cpc)) {
+			unblock_operations(sbi);
+			goto out;
+		}
+
 		if (NM_I(sbi)->dirty_nat_cnt == 0 &&
 				SIT_I(sbi)->dirty_sentries == 0 &&
 				prefree_segments(sbi) == 0) {

fs/f2fs/f2fs.h

@@ -2119,6 +2119,7 @@ void release_discard_addrs(struct f2fs_sb_info *);
 int npages_for_summary_flush(struct f2fs_sb_info *, bool);
 void allocate_new_segments(struct f2fs_sb_info *);
 int f2fs_trim_fs(struct f2fs_sb_info *, struct fstrim_range *);
+bool exist_trim_candidates(struct f2fs_sb_info *, struct cp_control *);
 struct page *get_sum_page(struct f2fs_sb_info *, unsigned int);
 void update_meta_page(struct f2fs_sb_info *, void *, block_t);
 void write_meta_page(struct f2fs_sb_info *, struct page *);

fs/f2fs/segment.c

@@ -834,7 +834,8 @@ static void __add_discard_entry(struct f2fs_sb_info *sbi,
 	SM_I(sbi)->nr_discards += end - start;
 }
 
-static void add_discard_addrs(struct f2fs_sb_info *sbi, struct cp_control *cpc)
+static bool add_discard_addrs(struct f2fs_sb_info *sbi, struct cp_control *cpc,
+							bool check_only)
 {
 	int entries = SIT_VBLOCK_MAP_SIZE / sizeof(unsigned long);
 	int max_blocks = sbi->blocks_per_seg;
@@ -848,12 +849,12 @@ static void add_discard_addrs(struct f2fs_sb_info *sbi, struct cp_control *cpc)
 	int i;
 
 	if (se->valid_blocks == max_blocks || !f2fs_discard_en(sbi))
-		return;
+		return false;
 
 	if (!force) {
 		if (!test_opt(sbi, DISCARD) || !se->valid_blocks ||
 		    SM_I(sbi)->nr_discards >= SM_I(sbi)->max_discards)
-			return;
+			return false;
 	}
 
 	/* SIT_VBLOCK_MAP_SIZE should be multiple of sizeof(unsigned long) */
@@ -871,8 +872,12 @@ static void add_discard_addrs(struct f2fs_sb_info *sbi, struct cp_control *cpc)
 					&& (end - start) < cpc->trim_minlen)
 			continue;
 
+		if (check_only)
+			return true;
+
 		__add_discard_entry(sbi, cpc, se, start, end);
 	}
+	return false;
 }
 
 void release_discard_addrs(struct f2fs_sb_info *sbi)
@@ -1453,6 +1458,24 @@ static const struct segment_allocation default_salloc_ops = {
 	.allocate_segment = allocate_segment_by_default,
 };
 
+bool exist_trim_candidates(struct f2fs_sb_info *sbi, struct cp_control *cpc)
+{
+	__u64 trim_start = cpc->trim_start;
+	bool has_candidate = false;
+
+	mutex_lock(&SIT_I(sbi)->sentry_lock);
+	for (; cpc->trim_start <= cpc->trim_end; cpc->trim_start++) {
+		if (add_discard_addrs(sbi, cpc, true)) {
+			has_candidate = true;
+			break;
+		}
+	}
+	mutex_unlock(&SIT_I(sbi)->sentry_lock);
+
+	cpc->trim_start = trim_start;
+	return has_candidate;
+}
+
 int f2fs_trim_fs(struct f2fs_sb_info *sbi, struct fstrim_range *range)
 {
 	__u64 start = F2FS_BYTES_TO_BLK(range->start);
@@ -2249,7 +2272,7 @@ void flush_sit_entries(struct f2fs_sb_info *sbi, struct cp_control *cpc)
 			/* add discard candidates */
 			if (cpc->reason != CP_DISCARD) {
 				cpc->trim_start = segno;
-				add_discard_addrs(sbi, cpc);
+				add_discard_addrs(sbi, cpc, false);
 			}
 
 			if (to_journal) {
@@ -2287,7 +2310,7 @@ void flush_sit_entries(struct f2fs_sb_info *sbi, struct cp_control *cpc)
 		__u64 trim_start = cpc->trim_start;
 
 		for (; cpc->trim_start <= cpc->trim_end; cpc->trim_start++)
-			add_discard_addrs(sbi, cpc);
+			add_discard_addrs(sbi, cpc, false);
 
 		cpc->trim_start = trim_start;
 	}