f2fs: introduce a periodic checkpoint flow

This patch introduces a periodic checkpoint feature.
Note that, this is not enforcing to conduct checkpoints very strictly in terms
of trigger timing, instead just hope to help user experiences.
The default value is 60 seconds.
Reviewed-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Documentation/ABI/testing/sysfs-fs-f2fs

@@ -80,3 +80,9 @@ Date:		February 2015
 Contact:	"Jaegeuk Kim" <jaegeuk@kernel.org>
 Description:
 		 Controls the trimming rate in batch mode.
+
+What:		/sys/fs/f2fs/<disk>/cp_interval
+Date:		October 2015
+Contact:	"Jaegeuk Kim" <jaegeuk@kernel.org>
+Description:
+		 Controls the checkpoint timing.

fs/f2fs/checkpoint.c

@@ -1114,6 +1114,9 @@ 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");

fs/f2fs/f2fs.h

@@ -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 */
 

fs/f2fs/segment.c

@@ -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);
 }
 

fs/f2fs/super.c

@@ -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);
@@ -1350,6 +1353,8 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
 		f2fs_commit_super(sbi, true);
 	}
 
+	sbi->cp_expires = round_jiffies_up(jiffies);
+
 	return 0;
 
 free_kobj: