Re: [PATCH v2 2/2] block: use a per disk workqueue for zone write plugging

[Christoph Hellwig <hch@infradead.org>]

On Sat, Apr 20, 2024 at 04:58:11PM +0900, Damien Le Moal wrote:
> A zone write plug BIO work function blk_zone_wplug_bio_work() calls
> submit_bio_noacct_nocheck() to execute the next unplugged BIO. This
> function may block. So executing zone plugs BIO works using the block
> layer global kblockd workqueue can potentially lead to preformance or
> latency issues as the number of concurrent work for a workqueue is
> limited to WQ_DFL_ACTIVE (256).
> 1) For a system with a large number of zoned disks, issuing write
>    requests to otherwise unused zones may be delayed wiating for a work
>    thread to become available.
> 2) Requeue operations which use kblockd but are independent of zone
>    write plugging may alsoi end up being delayed.
> 
> To avoid these potential performance issues, create a workqueue per
> zoned device to execute zone plugs BIO work. The workqueue max active
> parameter is set to the maximum number of zone write plugs allocated
> with the zone write plug mempool. This limit is equal to the maximum
> number of open zones of the disk and defaults to 128 for disks that do
> not have a limit on the number of open zones.

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Should the zone write plug submission do non-blocking submissions as well
to avoid stalling in the workqueue thread all the time?