f2fs: define MIN_DISCARD_GRANULARITY macro

Do cleanup in f2fs_tuning_parameters() and __init_discard_policy(),
let's use macro instead of number.
Suggested-by: Chao Yu <chao@kernel.org>
Signed-off-by: Yangtao Li <frank.li@vivo.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/f2fs.h

@@ -329,6 +329,8 @@ struct discard_entry {
 	unsigned char discard_map[SIT_VBLOCK_MAP_SIZE];	/* segment discard bitmap */
 };
 
+/* minimum discard granularity, unit: block count */
+#define MIN_DISCARD_GRANULARITY		1
 /* default discard granularity of inner discard thread, unit: block count */
 #define DEFAULT_DISCARD_GRANULARITY		16
 /* default maximum discard granularity of ordered discard, unit: block count */

fs/f2fs/segment.c

@@ -1065,7 +1065,7 @@ static void __init_discard_policy(struct f2fs_sb_info *sbi,
 		dpolicy->sync = false;
 		dpolicy->ordered = true;
 		if (utilization(sbi) > DEF_DISCARD_URGENT_UTIL) {
-			dpolicy->granularity = 1;
+			dpolicy->granularity = MIN_DISCARD_GRANULARITY;
 			if (atomic_read(&dcc->discard_cmd_cnt))
 				dpolicy->max_interval =
 					dcc->min_discard_issue_time;
@@ -1080,7 +1080,7 @@ static void __init_discard_policy(struct f2fs_sb_info *sbi,
 	} else if (discard_type == DPOLICY_UMOUNT) {
 		dpolicy->io_aware = false;
 		/* we need to issue all to keep CP_TRIMMED_FLAG */
-		dpolicy->granularity = 1;
+		dpolicy->granularity = MIN_DISCARD_GRANULARITY;
 		dpolicy->timeout = true;
 	}
 }

fs/f2fs/super.c

@@ -4080,7 +4080,8 @@ static void f2fs_tuning_parameters(struct f2fs_sb_info *sbi)
 	/* adjust parameters according to the volume size */
 	if (MAIN_SEGS(sbi) <= SMALL_VOLUME_SEGMENTS) {
 		if (f2fs_block_unit_discard(sbi))
-			SM_I(sbi)->dcc_info->discard_granularity = 1;
+			SM_I(sbi)->dcc_info->discard_granularity =
+						MIN_DISCARD_GRANULARITY;
 		SM_I(sbi)->ipu_policy = 1 << F2FS_IPU_FORCE |
 					1 << F2FS_IPU_HONOR_OPU_WRITE;
 	}