On 8/10/23 05:23, Bart Van Assche wrote:
> Writes in sequential write required zones must happen at the write
> pointer. Even if the submitter of the write commands (e.g. a filesystem)
> submits writes for sequential write required zones in order, the block
> layer or the storage controller may reorder these write commands.
>
> The zone locking mechanism in the mq-deadline I/O scheduler serializes
> write commands for sequential zones. Some but not all storage controllers
> require this serialization. Introduce a new request queue limit member
> variable to allow block drivers to indicate that they preserve the order
> of write commands and thus do not require serialization of writes per
> zone.
>
> Cc: Damien Le Moal <dlemoal@xxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Ming Lei <ming.lei@xxxxxxxxxx>
> Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
> ---
> block/blk-settings.c | 6 ++++++
> include/linux/blkdev.h | 1 +
> 2 files changed, 7 insertions(+)
>
> diff --git a/block/blk-settings.c b/block/blk-settings.c
> index 0046b447268f..b75c97971860 100644
> --- a/block/blk-settings.c
> +++ b/block/blk-settings.c
> @@ -56,6 +56,7 @@ void blk_set_default_limits(struct queue_limits *lim)
> lim->alignment_offset = 0;
> lim->io_opt = 0;
> lim->misaligned = 0;
> + lim->use_zone_write_lock = true;
> lim->zoned = BLK_ZONED_NONE;
Given that the default for zoned is BLK_ZONED_NONE, having use_zone_write_lock
default to true is strange. It would be better to set the default to false and
have disk_set_zoned() set it to true if needed, with an additional argument to
specify if it should be the case or not. E.g., for SMR drives, sd.c would call
something like:
disk_set_zoned(sdkp->disk, BLK_ZONED_HM, sdp->use_zone_write_lock);
sd.c would default to sdp->use_zone_write_lock == true and UFS driver can set
it to false. That would be cleaner I think.
> lim->zone_write_granularity = 0;
> lim->dma_alignment = 511;
> @@ -685,6 +686,11 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
> b->max_secure_erase_sectors);
> t->zone_write_granularity = max(t->zone_write_granularity,
> b->zone_write_granularity);
> + /*
> + * Whether or not the zone write lock should be used depends on the
> + * bottom driver only.
> + */
> + t->use_zone_write_lock = b->use_zone_write_lock;
Given that DM bio targets do not have a scheduler and do not have a zone lock
bitmap allocated, I do not think this is necessary at all. This can remain to
false, thus in sync with the fact that there is no IO scheduler.
> t->zoned = max(t->zoned, b->zoned);
> return ret;
> }
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 2f5371b8482c..deffa1f13444 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -316,6 +316,7 @@ struct queue_limits {
> unsigned char misaligned;
> unsigned char discard_misaligned;
> unsigned char raid_partial_stripes_expensive;
> + bool use_zone_write_lock;
> enum blk_zoned_model zoned;
>
> /*
--
Damien Le Moal
Western Digital Research
