Re: [PATCH v4 07/13] btrfs: zoned: use generic btrfs zone helpers to support npo2 zoned devices

Naohiro Aota
2022-05-19T04:13:36Z

On Mon, May 16, 2022 at 06:54:10PM +0200, Pankaj Raghav wrote:
> Add helpers to calculate alignment, round up and round down
> for zoned devices. These helpers encapsulates the necessary handling for
> power_of_2 and non-power_of_2 zone sizes. Optimized calculations are
> performed for zone sizes that are power_of_2 with log and shifts.
>
> btrfs_zoned_is_aligned() is added instead of reusing bdev_zone_aligned()
> helper due to some use cases in btrfs where zone alignment is checked
> before having access to the underlying block device such as in this
> function: btrfs_load_block_group_zone_info().
>
> Use the generic btrfs zone helpers to calculate zone index, check zone
> alignment, round up and round down operations.
>
> The zone_size_shift field is not needed anymore as generic helpers are
> used for calculation.
>
> Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
> ---
> fs/btrfs/volumes.c | 24 +++++++++-------
> fs/btrfs/zoned.c | 72 ++++++++++++++++++++++------------------------
> fs/btrfs/zoned.h | 43 +++++++++++++++++++++++----
> 3 files changed, 85 insertions(+), 54 deletions(-)
>
><snip>
> diff --git a/fs/btrfs/zoned.h b/fs/btrfs/zoned.h
> index 694ab6d1e..b94ce4d1f 100644
> --- a/fs/btrfs/zoned.h
> +++ b/fs/btrfs/zoned.h
> @@ -9,6 +9,7 @@
> #include "disk-io.h"
> #include "block-group.h"
> #include "btrfs_inode.h"
> +#include "misc.h"
>
> #define BTRFS_DEFAULT_RECLAIM_THRESH (75)
>
> @@ -18,7 +19,6 @@ struct btrfs_zoned_device_info {
> * zoned block device.
> */
> u64 zone_size;
> - u8 zone_size_shift;
> u32 nr_zones;
> unsigned int max_active_zones;
> atomic_t active_zones_left;
> @@ -30,6 +30,36 @@ struct btrfs_zoned_device_info {
> u32 sb_zone_location[BTRFS_SUPER_MIRROR_MAX];
> };
>
> +static inline bool btrfs_zoned_is_aligned(u64 pos, u64 zone_size)
> +{
> + u64 remainder = 0;
> +
> + if (is_power_of_two_u64(zone_size))
> + return IS_ALIGNED(pos, zone_size);
> +
> + div64_u64_rem(pos, zone_size, &remainder);
> + return remainder == 0;
> +}
> +
> +static inline u64 btrfs_zoned_roundup(u64 pos, u64 zone_size)
> +{
> + if (is_power_of_two_u64(zone_size))
> + return ALIGN(pos, zone_size);
> +
> + return div64_u64(pos + zone_size - 1, zone_size) * zone_size;
> +}
> +
> +static inline u64 btrfs_zoned_rounddown(u64 pos, u64 zone_size)
> +{
> + u64 remainder = 0;
> + if (is_power_of_two_u64(zone_size))
> + return round_down(pos, zone_size);
> +
> + div64_u64_rem(pos, zone_size, &remainder);
> + pos -= remainder;
> + return pos;
> +}
> +

This is just a preference, but how about naming these helpers not related
to "zoned"? While they take "zone_size" as an argument, it does not do
anything special on zoned things. For my preference, I would take
btrfs_device or btrfs_zoned_device_info for "btrfs_zoned_*" function.

Actually, I was a bit confused seeing the part
below. btrfs_zoned_is_aligned() takes "sector_t" values while the arguments
are often byte granularity address. Yeah, actually sector_t == u64 and the
code does not relies on the unit ... so, it is OK as long as the values are
in the same unit.

@@ -409,9 +409,8 @@ int btrfs_get_dev_zone_info(struct btrfs_device *device, bool populate_cache)
}

nr_sectors = bdev_nr_sectors(bdev);
- zone_info->zone_size_shift = ilog2(zone_info->zone_size);
- zone_info->nr_zones = nr_sectors >> ilog2(zone_sectors);
- if (!IS_ALIGNED(nr_sectors, zone_sectors))
+ zone_info->nr_zones = bdev_zone_no(bdev, nr_sectors);
+ if (!btrfs_zoned_is_aligned(nr_sectors, zone_sectors))
zone_info->nr_zones++;

max_active_zones = bdev_max_active_zones(bdev);

BTW, aren't these helpers used in other subsystems? Maybe adding these in
include/linux/math64.h or so?