Re: [PATCH v2] nvme: remove namespaces in parallel

[Hannes Reinecke]

On 11/3/26 7:28 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@xxxxxxxxx>
> ---
> V1 -> V2:
> - Explain why removing the namespaces in parallel saves time
> - Drop patch 2 until the elevator switch locking change settles:
>    https://lore.kernel.org/r/20261031044141.5569-1-laveeshb@xxxxxxxxxxxxxxxxx
>
> v1: https://lore.kernel.org/r/20261102-bug-nvme-remove-ns-async-v1-0-61780fee111c@xxxxxxxxx
> ---
>   drivers/nvme/host/core.c | 13 ++++++++++++-
>   1 file changed, 12 insertions(+), 1 deletion(-)
Reviewed-by: Hannes Reinecke <hare@xxxxxxxxxx>

Cheers,

Hannes
--
Dr. Hannes Reinecke                  Kernel Storage Architect
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