f2fs: add to account skip count of background GC

This patch adds to account skip count of background GC, and show stat
info via 'status' debugfs entry.
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/debug.c

@@ -101,6 +101,8 @@ static void update_general_status(struct f2fs_sb_info *sbi)
 	si->avail_nids = NM_I(sbi)->available_nids;
 	si->alloc_nids = NM_I(sbi)->nid_cnt[PREALLOC_NID];
 	si->bg_gc = sbi->bg_gc;
+	si->io_skip_bggc = sbi->io_skip_bggc;
+	si->other_skip_bggc = sbi->other_skip_bggc;
 	si->skipped_atomic_files[BG_GC] = sbi->skipped_atomic_files[BG_GC];
 	si->skipped_atomic_files[FG_GC] = sbi->skipped_atomic_files[FG_GC];
 	si->util_free = (int)(free_user_blocks(sbi) >> sbi->log_blocks_per_seg)
@@ -355,6 +357,8 @@ static int stat_show(struct seq_file *s, void *v)
 				si->skipped_atomic_files[BG_GC] +
 				si->skipped_atomic_files[FG_GC],
 				si->skipped_atomic_files[BG_GC]);
+		seq_printf(s, "BG skip : IO: %u, Other: %u\n",
+				si->io_skip_bggc, si->other_skip_bggc);
 		seq_puts(s, "\nExtent Cache:\n");
 		seq_printf(s, "  - Hit Count: L1-1:%llu L1-2:%llu L2:%llu\n",
 				si->hit_largest, si->hit_cached,

fs/f2fs/f2fs.h

@@ -1277,6 +1277,8 @@ struct f2fs_sb_info {
 	atomic_t max_aw_cnt;			/* max # of atomic writes */
 	atomic_t max_vw_cnt;			/* max # of volatile writes */
 	int bg_gc;				/* background gc calls */
+	unsigned int io_skip_bggc;		/* skip background gc for in-flight IO */
+	unsigned int other_skip_bggc;		/* skip background gc for other reasons */
 	unsigned int ndirty_inode[NR_INODE_TYPE];	/* # of dirty inodes */
 #endif
 	spinlock_t stat_lock;			/* lock for stat operations */
@@ -3104,6 +3106,7 @@ struct f2fs_stat_info {
 	int free_nids, avail_nids, alloc_nids;
 	int total_count, utilization;
 	int bg_gc, nr_wb_cp_data, nr_wb_data;
+	unsigned int io_skip_bggc, other_skip_bggc;
 	int nr_flushing, nr_flushed, flush_list_empty;
 	int nr_discarding, nr_discarded;
 	int nr_discard_cmd;
@@ -3141,6 +3144,8 @@ static inline struct f2fs_stat_info *F2FS_STAT(struct f2fs_sb_info *sbi)
 #define stat_inc_bg_cp_count(si)	((si)->bg_cp_count++)
 #define stat_inc_call_count(si)		((si)->call_count++)
 #define stat_inc_bggc_count(sbi)	((sbi)->bg_gc++)
+#define stat_io_skip_bggc_count(sbi)	((sbi)->io_skip_bggc++)
+#define stat_other_skip_bggc_count(sbi)	((sbi)->other_skip_bggc++)
 #define stat_inc_dirty_inode(sbi, type)	((sbi)->ndirty_inode[type]++)
 #define stat_dec_dirty_inode(sbi, type)	((sbi)->ndirty_inode[type]--)
 #define stat_inc_total_hit(sbi)		(atomic64_inc(&(sbi)->total_hit_ext))
@@ -3257,6 +3262,8 @@ void f2fs_destroy_root_stats(void);
 #define stat_inc_bg_cp_count(si)			do { } while (0)
 #define stat_inc_call_count(si)				do { } while (0)
 #define stat_inc_bggc_count(si)				do { } while (0)
+#define stat_io_skip_bggc_count(sbi)			do { } while (0)
+#define stat_other_skip_bggc_count(sbi)			do { } while (0)
 #define stat_inc_dirty_inode(sbi, type)			do { } while (0)
 #define stat_dec_dirty_inode(sbi, type)			do { } while (0)
 #define stat_inc_total_hit(sb)				do { } while (0)

fs/f2fs/gc.c

@@ -40,13 +40,16 @@ static int gc_thread_func(void *data)
 		if (gc_th->gc_wake)
 			gc_th->gc_wake = 0;
 
-		if (try_to_freeze())
+		if (try_to_freeze()) {
+			stat_other_skip_bggc_count(sbi);
 			continue;
+		}
 		if (kthread_should_stop())
 			break;
 
 		if (sbi->sb->s_writers.frozen >= SB_FREEZE_WRITE) {
 			increase_sleep_time(gc_th, &wait_ms);
+			stat_other_skip_bggc_count(sbi);
 			continue;
 		}
 
@@ -55,8 +58,10 @@ static int gc_thread_func(void *data)
 			f2fs_stop_checkpoint(sbi, false);
 		}
 
-		if (!sb_start_write_trylock(sbi->sb))
+		if (!sb_start_write_trylock(sbi->sb)) {
+			stat_other_skip_bggc_count(sbi);
 			continue;
+		}
 
 		/*
 		 * [GC triggering condition]
@@ -77,12 +82,15 @@ static int gc_thread_func(void *data)
 			goto do_gc;
 		}
 
-		if (!mutex_trylock(&sbi->gc_mutex))
+		if (!mutex_trylock(&sbi->gc_mutex)) {
+			stat_other_skip_bggc_count(sbi);
 			goto next;
+		}
 
 		if (!is_idle(sbi, GC_TIME)) {
 			increase_sleep_time(gc_th, &wait_ms);
 			mutex_unlock(&sbi->gc_mutex);
+			stat_io_skip_bggc_count(sbi);
 			goto next;
 		}