f2fs: introduce discard_granularity sysfs entry

Commit d618ebaf0aa8 ("f2fs: enable small discard by default") enables
f2fs to issue 4K size discard in real-time discard mode. However, issuing
smaller discard may cost more lifetime but releasing less free space in
flash device. Since f2fs has ability of separating hot/cold data and
garbage collection, we can expect that small-sized invalid region would
expand soon with OPU, deletion or garbage collection on valid datas, so
it's better to delay or skip issuing smaller size discards, it could help
to reduce overmuch consumption of IO bandwidth and lifetime of flash
storage.

This patch makes f2fs selectng 64K size as its default minimal
granularity, and issue discard with the size which is not smaller than
minimal granularity. Also it exposes discard granularity as sysfs entry
for configuration in different scenario.

Jaegeuk Kim:
 We must issue all the accumulated discard commands when fstrim is called.
 So, I've added pend_list_tag[] to indicate whether we should issue the
 commands or not. If tag sets P_ACTIVE or P_TRIM, we have to issue them.
 P_TRIM is set once at a time, given fstrim trigger.
 In addition, issue_discard_thread is calling too much due to the number of
 discard commands remaining in the pending list. I added a timer to control
 it likewise gc_thread.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

1 files changed, 12 insertions, 0 deletions

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index e252e5bf9791..4b993961d81d 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -148,6 +148,8 @@ enum {
 		(BATCHED_TRIM_SEGMENTS(sbi) << (sbi)->log_blocks_per_seg)
 #define MAX_DISCARD_BLOCKS(sbi)		BLKS_PER_SEC(sbi)
 #define DISCARD_ISSUE_RATE		8
+#define DEF_MIN_DISCARD_ISSUE_TIME	50	/* 50 ms, if exists */
+#define DEF_MAX_DISCARD_ISSUE_TIME	60000	/* 60 s, if no candidates */
 #define DEF_CP_INTERVAL			60	/* 60 secs */
 #define DEF_IDLE_INTERVAL		5	/* 5 secs */
 
@@ -196,11 +198,18 @@ struct discard_entry {
 	unsigned char discard_map[SIT_VBLOCK_MAP_SIZE];	/* segment discard bitmap */
 };
 
+/* default discard granularity of inner discard thread, unit: block count */
+#define DEFAULT_DISCARD_GRANULARITY		16
+
 /* max discard pend list number */
 #define MAX_PLIST_NUM		512
 #define plist_idx(blk_num)	((blk_num) >= MAX_PLIST_NUM ?		\
 					(MAX_PLIST_NUM - 1) : (blk_num - 1))
 
+#define P_ACTIVE	0x01
+#define P_TRIM		0x02
+#define plist_issue(tag)	(((tag) & P_ACTIVE) || ((tag) & P_TRIM))
+
 enum {
 	D_PREP,
 	D_SUBMIT,
@@ -236,11 +245,14 @@ struct discard_cmd_control {
 	struct task_struct *f2fs_issue_discard;	/* discard thread */
 	struct list_head entry_list;		/* 4KB discard entry list */
 	struct list_head pend_list[MAX_PLIST_NUM];/* store pending entries */
+	unsigned char pend_list_tag[MAX_PLIST_NUM];/* tag for pending entries */
 	struct list_head wait_list;		/* store on-flushing entries */
 	wait_queue_head_t discard_wait_queue;	/* waiting queue for wake-up */
+	unsigned int discard_wake;		/* to wake up discard thread */
 	struct mutex cmd_lock;
 	unsigned int nr_discards;		/* # of discards in the list */
 	unsigned int max_discards;		/* max. discards to be issued */
+	unsigned int discard_granularity;	/* discard granularity */
 	unsigned int undiscard_blks;		/* # of undiscard blocks */
 	atomic_t issued_discard;		/* # of issued discard */
 	atomic_t issing_discard;		/* # of issing discard */