[PATCH v2] nvme: remove namespaces in parallel

[Nilay Shroff]

On 11/3/26 11:58 AM, Qiliang Yuan wrote:
> nvme_remove_namespaces() removes the namespaces of a controller one
> after another. Each removal waits for RCU grace periods in
> del_gendisk() for the namespace and for its multipath head, about
> 20 ms in all.
> 
> Deleting a controller, such as disconnecting from a fabrics target,
> thus takes time proportional to its namespace count, over a second for
> 64 namespaces. Scanning had the same problem until commit 4e893ca81170
> ("nvme_core: scan namespaces asynchronously") made it add namespaces
> in parallel.
> 
> Remove the namespaces through an async domain the same way, and wait
> for all of them before returning. Each removal still waits about
> 20 ms, but the waits now overlap: a grace period is system-wide, so
> removals that wait at the same time are released by the same grace
> periods instead of each needing its own.
> 
> Disconnect time from a target on the same host, over tcp to 127.0.0.1
> and over nvme-loop, with 4 I/O queues, median of 3 runs on each of two
> boots per kernel:
> 
>    namespaces  transport  before              after
>             8  tcp         170 /  171 ms        85 /   91 ms
>            32  tcp         628 /  628 ms       294 /  293 ms
>            64  tcp        1201 / 1308 ms       533 /  550 ms
>            64  loop       1988 / 1913 ms      1283 / 1200 ms
> 
> Signed-off-by: Qiliang Yuan<odys.yuan at gmail.com>

Looks good to me:
Reviewed-by: Nilay Shroff <nilay at linux.ibm.com>