f2fs: introduce discard_urgent_util sysfs node

Through this node, you can control the background discard
to run more aggressively or not aggressively when reach the
utilization rate of the space.
Signed-off-by: Yangtao Li <frank.li@vivo.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Documentation/ABI/testing/sysfs-fs-f2fs

@@ -647,3 +647,11 @@ Date:		October 2022
 Contact:	"Yangtao Li" <frank.li@vivo.com>
 Description:	Show the current gc_mode as a string.
 		This is a read-only entry.
+
+What:		/sys/fs/f2fs/<disk>/discard_urgent_util
+Date:		November 2022
+Contact:	"Yangtao Li" <frank.li@vivo.com>
+Description:	When space utilization exceeds this, do background DISCARD aggressively.
+		Does DISCARD forcibly in a period of given min_discard_issue_time when the number
+		of discards is not 0 and set discard granularity to 1.
+		Default: 80

fs/f2fs/f2fs.h

@@ -413,6 +413,7 @@ struct discard_cmd_control {
 	unsigned int min_discard_issue_time;	/* min. interval between discard issue */
 	unsigned int mid_discard_issue_time;	/* mid. interval between discard issue */
 	unsigned int max_discard_issue_time;	/* max. interval between discard issue */
+	unsigned int discard_urgent_util;	/* utilization which issue discard proactively */
 	unsigned int discard_granularity;	/* discard granularity */
 	unsigned int max_ordered_discard;	/* maximum discard granularity issued by lba order */
 	unsigned int undiscard_blks;		/* # of undiscard blocks */

fs/f2fs/segment.c

@@ -1064,7 +1064,7 @@ static void __init_discard_policy(struct f2fs_sb_info *sbi,
 		dpolicy->io_aware = true;
 		dpolicy->sync = false;
 		dpolicy->ordered = true;
-		if (utilization(sbi) > DEF_DISCARD_URGENT_UTIL) {
+		if (utilization(sbi) > dcc->discard_urgent_util) {
 			dpolicy->granularity = MIN_DISCARD_GRANULARITY;
 			if (atomic_read(&dcc->discard_cmd_cnt))
 				dpolicy->max_interval =
@@ -2079,6 +2079,7 @@ static int create_discard_cmd_control(struct f2fs_sb_info *sbi)
 	dcc->min_discard_issue_time = DEF_MIN_DISCARD_ISSUE_TIME;
 	dcc->mid_discard_issue_time = DEF_MID_DISCARD_ISSUE_TIME;
 	dcc->max_discard_issue_time = DEF_MAX_DISCARD_ISSUE_TIME;
+	dcc->discard_urgent_util = DEF_DISCARD_URGENT_UTIL;
 	dcc->undiscard_blks = 0;
 	dcc->next_pos = 0;
 	dcc->root = RB_ROOT_CACHED;

fs/f2fs/sysfs.c

@@ -493,6 +493,13 @@ static ssize_t __sbi_store(struct f2fs_attr *a,
 		return count;
 	}
 
+	if (!strcmp(a->attr.name, "discard_urgent_util")) {
+		if (t > 100)
+			return -EINVAL;
+		*ui = t;
+		return count;
+	}
+
 	if (!strcmp(a->attr.name, "migration_granularity")) {
 		if (t == 0 || t > sbi->segs_per_sec)
 			return -EINVAL;
@@ -800,6 +807,7 @@ F2FS_RW_ATTR(DCC_INFO, discard_cmd_control, max_discard_request, max_discard_req
 F2FS_RW_ATTR(DCC_INFO, discard_cmd_control, min_discard_issue_time, min_discard_issue_time);
 F2FS_RW_ATTR(DCC_INFO, discard_cmd_control, mid_discard_issue_time, mid_discard_issue_time);
 F2FS_RW_ATTR(DCC_INFO, discard_cmd_control, max_discard_issue_time, max_discard_issue_time);
+F2FS_RW_ATTR(DCC_INFO, discard_cmd_control, discard_urgent_util, discard_urgent_util);
 F2FS_RW_ATTR(DCC_INFO, discard_cmd_control, discard_granularity, discard_granularity);
 F2FS_RW_ATTR(DCC_INFO, discard_cmd_control, max_ordered_discard, max_ordered_discard);
 F2FS_RW_ATTR(RESERVED_BLOCKS, f2fs_sb_info, reserved_blocks, reserved_blocks);
@@ -930,6 +938,7 @@ static struct attribute *f2fs_attrs[] = {
 	ATTR_LIST(min_discard_issue_time),
 	ATTR_LIST(mid_discard_issue_time),
 	ATTR_LIST(max_discard_issue_time),
+	ATTR_LIST(discard_urgent_util),
 	ATTR_LIST(discard_granularity),
 	ATTR_LIST(max_ordered_discard),
 	ATTR_LIST(pending_discard),