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>
diff --git a/Documentation/ABI/testing/sysfs-fs-f2fs b/Documentation/ABI/testing/sysfs-fs-f2fs
index 2c4cc42..e066281d 100644
--- a/Documentation/ABI/testing/sysfs-fs-f2fs
+++ b/Documentation/ABI/testing/sysfs-fs-f2fs
@@ -80,3 +80,9 @@
 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.
diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index ff53405..0569097 100644
--- a/fs/f2fs/checkpoint.c
+++ b/fs/f2fs/checkpoint.c
@@ -1114,6 +1114,9 @@
 	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");
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 00bd470..aad4720 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -124,6 +124,7 @@
 		(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 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 */
 
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 6b8edf2..1d86a35 100644
--- a/fs/f2fs/segment.c
+++ b/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 @@
 	/* 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);
 }
 
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index ba058d0..cb23d85 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -215,6 +215,7 @@
 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 @@
 	ATTR_LIST(max_victim_search),
 	ATTR_LIST(dir_level),
 	ATTR_LIST(ram_thresh),
+	ATTR_LIST(cp_interval),
 	NULL,
 };
 
@@ -1014,6 +1016,7 @@
 		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 @@
 		f2fs_commit_super(sbi, true);
 	}
 
+	sbi->cp_expires = round_jiffies_up(jiffies);
+
 	return 0;
 
 free_kobj: