f2fs: Reduce zoned block device memory usage

For zoned block devices, an array of zone types for each device is
allocated and initialized in order to determine if a section is stored
on a sequential zone (zone reset needed) or a conventional zone (no
zone reset needed and regular discard applies). Considering this usage,
the zone types stored in memory can be replaced with a bitmap to
indicate an equivalent information, that is, if a zone is sequential or
not. This reduces the memory usage for each zoned device by roughly 8:
on a 14TB disk with zones of 256 MB, the zone type array consumes
13x4KB pages while the bitmap uses only 2x4KB pages.

This patch changes the f2fs_dev_info structure blkz_type field to the
bitmap blkz_seq. Access to this bitmap is done using the helper
function f2fs_blkz_is_seq(), which is a rewrite of the function
get_blkz_type().

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/f2fs.h

@@ -1068,8 +1068,8 @@ struct f2fs_dev_info {
 	block_t start_blk;
 	block_t end_blk;
 #ifdef CONFIG_BLK_DEV_ZONED
-	unsigned int nr_blkz;			/* Total number of zones */
-	u8 *blkz_type;				/* Array of zones type */
+	unsigned int nr_blkz;		/* Total number of zones */
+	unsigned long *blkz_seq;	/* Bitmap indicating sequential zones */
 #endif
 };
 
@@ -3542,16 +3542,12 @@ F2FS_FEATURE_FUNCS(lost_found, LOST_FOUND);
 F2FS_FEATURE_FUNCS(sb_chksum, SB_CHKSUM);
 
 #ifdef CONFIG_BLK_DEV_ZONED
-static inline int get_blkz_type(struct f2fs_sb_info *sbi,
-			struct block_device *bdev, block_t blkaddr)
+static inline bool f2fs_blkz_is_seq(struct f2fs_sb_info *sbi, int devi,
+				    block_t blkaddr)
 {
 	unsigned int zno = blkaddr >> sbi->log_blocks_per_blkz;
-	int i;
 
-	for (i = 0; i < sbi->s_ndevs; i++)
-		if (FDEV(i).bdev == bdev)
-			return FDEV(i).blkz_type[zno];
-	return -EINVAL;
+	return test_bit(zno, FDEV(devi).blkz_seq);
 }
 #endif