f2fs: introduce background_gc=sync mount option

index 18e5902..00bd470 100644
@@ -53,6 +53,7 @@
 #define F2FS_MOUNT_NOBARRIER		0x00000800
 #define F2FS_MOUNT_FASTBOOT		0x00001000
 #define F2FS_MOUNT_EXTENT_CACHE		0x00002000
+#define F2FS_MOUNT_FORCE_FG_GC		0x00004000
 
 #define clear_opt(sbi, option)	(sbi->mount_opt.opt &= ~F2FS_MOUNT_##option)
 #define set_opt(sbi, option)	(sbi->mount_opt.opt |= F2FS_MOUNT_##option)

index 830d277..e627c19 100644
@@ -78,7 +78,7 @@ static int gc_thread_func(void *data)
 		stat_inc_bggc_count(sbi);
 
 		/* if return value is not zero, no victim was selected */
-		if (f2fs_gc(sbi, false))
+		if (f2fs_gc(sbi, test_opt(sbi, FORCE_FG_GC)))
 			wait_ms = gc_th->no_gc_sleep_time;
 
 		/* balancing f2fs's metadata periodically */

index a294da7..e9afb58 100644
@@ -137,10 +137,12 @@ enum {
 /*
  * BG_GC means the background cleaning job.
  * FG_GC means the on-demand cleaning job.
+ * FORCE_FG_GC means on-demand cleaning job in background.
  */
 enum {
 	BG_GC = 0,
-	FG_GC
+	FG_GC,
+	FORCE_FG_GC,
 };
 
 /* for a function parameter to select a victim segment */

index 16442ec..ba058d0 100644
@@ -292,11 +292,16 @@ static int parse_options(struct super_block *sb, char *options)
 
 			if (!name)
 				return -ENOMEM;
-			if (strlen(name) == 2 && !strncmp(name, "on", 2))
+			if (strlen(name) == 2 && !strncmp(name, "on", 2)) {
 				set_opt(sbi, BG_GC);
-			else if (strlen(name) == 3 && !strncmp(name, "off", 3))
+				clear_opt(sbi, FORCE_FG_GC);
+			} else if (strlen(name) == 3 && !strncmp(name, "off", 3)) {
 				clear_opt(sbi, BG_GC);
-			else {
+				clear_opt(sbi, FORCE_FG_GC);
+			} else if (strlen(name) == 4 && !strncmp(name, "sync", 4)) {
+				set_opt(sbi, BG_GC);
+				set_opt(sbi, FORCE_FG_GC);
+			} else {
 				kfree(name);
 				return -EINVAL;
 			}

@@ -631,10 +636,14 @@ static int f2fs_show_options(struct seq_file *seq, struct dentry *root)
 {
 	struct f2fs_sb_info *sbi = F2FS_SB(root->d_sb);
 
-	if (!f2fs_readonly(sbi->sb) && test_opt(sbi, BG_GC))
-		seq_printf(seq, ",background_gc=%s", "on");
-	else
+	if (!f2fs_readonly(sbi->sb) && test_opt(sbi, BG_GC)) {
+		if (test_opt(sbi, FORCE_FG_GC))
+			seq_printf(seq, ",background_gc=%s", "sync");
+		else
+			seq_printf(seq, ",background_gc=%s", "on");
+	} else {
 		seq_printf(seq, ",background_gc=%s", "off");
+	}
 	if (test_opt(sbi, DISABLE_ROLL_FORWARD))
 		seq_puts(seq, ",disable_roll_forward");
 	if (test_opt(sbi, DISCARD))

index e627c19..e7cec86 100644
@@ -77,6 +77,9 @@ static int gc_thread_func(void *data)
 
 		stat_inc_bggc_count(sbi);
 
+		trace_f2fs_background_gc(sbi->sb, wait_ms,
+				prefree_segments(sbi), free_segments(sbi));
+
 		/* if return value is not zero, no victim was selected */
 		if (f2fs_gc(sbi, test_opt(sbi, FORCE_FG_GC)))
 			wait_ms = gc_th->no_gc_sleep_time;

index 6aa63d9..7de751d 100644
@@ -514,6 +514,34 @@ TRACE_EVENT(f2fs_map_blocks,
 		__entry->ret)
 );
 
+TRACE_EVENT(f2fs_background_gc,
+
+	TP_PROTO(struct super_block *sb, long wait_ms,
+			unsigned int prefree, unsigned int free),
+
+	TP_ARGS(sb, wait_ms, prefree, free),
+
+	TP_STRUCT__entry(
+		__field(dev_t,	dev)
+		__field(long,	wait_ms)
+		__field(unsigned int,	prefree)
+		__field(unsigned int,	free)
+	),
+
+	TP_fast_assign(
+		__entry->dev		= sb->s_dev;
+		__entry->wait_ms	= wait_ms;
+		__entry->prefree	= prefree;
+		__entry->free		= free;
+	),
+
+	TP_printk("dev = (%d,%d), wait_ms = %ld, prefree = %u, free = %u",
+		show_dev(__entry),
+		__entry->wait_ms,
+		__entry->prefree,
+		__entry->free)
+);
+
 TRACE_EVENT(f2fs_get_victim,
 
 	TP_PROTO(struct super_block *sb, int type, int gc_type,

index af7c24c..fedbf67 100644
@@ -77,13 +77,13 @@ static int gc_thread_func(void *data)
 
 		stat_inc_bggc_count(sbi);
 
-		trace_f2fs_background_gc(sbi->sb, wait_ms,
-				prefree_segments(sbi), free_segments(sbi));
-
 		/* if return value is not zero, no victim was selected */
 		if (f2fs_gc(sbi, test_opt(sbi, FORCE_FG_GC)))
 			wait_ms = gc_th->no_gc_sleep_time;
 
+		trace_f2fs_background_gc(sbi->sb, wait_ms,
+				prefree_segments(sbi), free_segments(sbi));
+
 		/* balancing f2fs's metadata periodically */
 		f2fs_balance_fs_bg(sbi);
 

index da5ee7e..70a4780 100644
@@ -1120,6 +1120,9 @@ void write_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
 	if (cpc->reason == CP_RECOVERY)
 		f2fs_msg(sbi->sb, KERN_NOTICE,
 			"checkpoint: version = %llx", ckpt_ver);
+
+	/* do checkpoint periodically */
+	sbi->cp_expires = round_jiffies_up(jiffies + HZ * sbi->cp_interval);
 out:
 	mutex_unlock(&sbi->cp_mutex);
 	trace_f2fs_write_checkpoint(sbi->sb, cpc->reason, "finish checkpoint");

index 00bd470..aad4720 100644
@@ -124,6 +124,7 @@ enum {
 		(SM_I(sbi)->trim_sections * (sbi)->segs_per_sec)
 #define BATCHED_TRIM_BLOCKS(sbi)	\
 		(BATCHED_TRIM_SEGMENTS(sbi) << (sbi)->log_blocks_per_seg)
+#define DEF_CP_INTERVAL			60	/* 60 secs */
 
 struct cp_control {
 	int reason;

@@ -734,6 +735,7 @@ struct f2fs_sb_info {
 	struct rw_semaphore node_write;		/* locking node writes */
 	struct mutex writepages;		/* mutex for writepages() */
 	wait_queue_head_t cp_wait;
+	long cp_expires, cp_interval;		/* next expected periodic cp */
 
 	struct inode_management im[MAX_INO_ENTRY];      /* manage inode cache */
 

index 6b8edf2..1d86a35 100644
@@ -15,6 +15,7 @@
 #include <linux/prefetch.h>
 #include <linux/kthread.h>
 #include <linux/swap.h>
+#include <linux/timer.h>
 
 #include "f2fs.h"
 #include "segment.h"

@@ -315,7 +316,8 @@ void f2fs_balance_fs_bg(struct f2fs_sb_info *sbi)
 	/* checkpoint is the only way to shrink partial cached entries */
 	if (!available_free_memory(sbi, NAT_ENTRIES) ||
 			excess_prefree_segs(sbi) ||
-			!available_free_memory(sbi, INO_ENTRIES))
+			!available_free_memory(sbi, INO_ENTRIES) ||
+			jiffies > sbi->cp_expires)
 		f2fs_sync_fs(sbi->sb, true);
 }
 

index ba058d0..e275634 100644
@@ -215,6 +215,7 @@ F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, min_fsync_blocks, min_fsync_blocks);
 F2FS_RW_ATTR(NM_INFO, f2fs_nm_info, ram_thresh, ram_thresh);
 F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, max_victim_search, max_victim_search);
 F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, dir_level, dir_level);
+F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, cp_interval, cp_interval);
 
 #define ATTR_LIST(name) (&f2fs_attr_##name.attr)
 static struct attribute *f2fs_attrs[] = {

@@ -231,6 +232,7 @@ static struct attribute *f2fs_attrs[] = {
 	ATTR_LIST(max_victim_search),
 	ATTR_LIST(dir_level),
 	ATTR_LIST(ram_thresh),
+	ATTR_LIST(cp_interval),
 	NULL,
 };
 

@@ -1014,6 +1016,7 @@ static void init_sb_info(struct f2fs_sb_info *sbi)
 		atomic_set(&sbi->nr_pages[i], 0);
 
 	sbi->dir_level = DEF_DIR_LEVEL;
+	sbi->cp_interval = DEF_CP_INTERVAL;
 	clear_sbi_flag(sbi, SBI_NEED_FSCK);
 
 	INIT_LIST_HEAD(&sbi->s_list);