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

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Message-ID: <20220519041328.rcfd2jk6pslwvyfm@naota-xeon>
Date:   Thu, 19 May 2022 04:13:29 +0000
From:   Naohiro Aota <Naohiro.Aota@....com>
To:     Pankaj Raghav <p.raghav@...sung.com>
CC:     "axboe@...nel.dk" <axboe@...nel.dk>,
        "damien.lemoal@...nsource.wdc.com" <damien.lemoal@...nsource.wdc.com>,
        "pankydev8@...il.com" <pankydev8@...il.com>,
        "dsterba@...e.com" <dsterba@...e.com>, "hch@....de" <hch@....de>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>,
        "jiangbo.365@...edance.com" <jiangbo.365@...edance.com>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "gost.dev@...sung.com" <gost.dev@...sung.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dm-devel@...hat.com" <dm-devel@...hat.com>,
        Luis Chamberlain <mcgrof@...nel.org>
Subject: Re: [PATCH v4 07/13] btrfs: zoned: use generic btrfs zone helpers to
 support npo2 zoned devices

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@...nel.org>
> Signed-off-by: Pankaj Raghav <p.raghav@...sung.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?