* [PATCH] nvme: scan sequentially only when list scan unsupported
@ 2022-11-04 22:36 Uday Shankar
2022-11-04 22:46 ` Uday Shankar
2022-11-07 5:56 ` Christoph Hellwig
0 siblings, 2 replies; 4+ messages in thread
From: Uday Shankar @ 2022-11-04 22:36 UTC (permalink / raw)
To: linux-nvme
Cc: Christoph Hellwig, Keith Busch, Sagi Grimberg, Jens Axboe, Uday Shankar
Currently, if nvme_scan_ns_list fails, nvme_scan_work will fall back to
a sequential scan. nvme_scan_ns_list can fail for a variety of reasons,
e.g. transient transport issue. And the resulting sequential scan can be
extremely expensive on controllers reporting an NN value close to the
maximum allowed (>4 billion). Avoid sequential scans wherever possible
by only falling back to them if nvme_scan_ns_list fails due to
controller non-support of Identify NS List.
---
This would break devices that claim to support version NVME_VS(1, 1, 0)
or above, but don't support Identify NS List. But it looks like we
already have NVME_QUIRK_IDENTIFY_CNS to deal with that.
drivers/nvme/host/core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 0090dc0b3ae6..5bd19819d33b 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -4535,7 +4535,7 @@ static void nvme_scan_work(struct work_struct *work)
}
mutex_lock(&ctrl->scan_lock);
- if (nvme_scan_ns_list(ctrl) != 0)
+ if (nvme_scan_ns_list(ctrl) == -EOPNOTSUPP)
nvme_scan_ns_sequential(ctrl);
mutex_unlock(&ctrl->scan_lock);
}
base-commit: d30a909f9bb5283e701a5fdfffac763ef57a3e7c
--
2.25.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] nvme: scan sequentially only when list scan unsupported
2022-11-04 22:36 [PATCH] nvme: scan sequentially only when list scan unsupported Uday Shankar
@ 2022-11-04 22:46 ` Uday Shankar
2022-11-07 5:56 ` Christoph Hellwig
1 sibling, 0 replies; 4+ messages in thread
From: Uday Shankar @ 2022-11-04 22:46 UTC (permalink / raw)
To: linux-nvme; +Cc: Christoph Hellwig, Keith Busch, Sagi Grimberg, Jens Axboe
> Currently, if nvme_scan_ns_list fails, nvme_scan_work will fall back to
> a sequential scan. nvme_scan_ns_list can fail for a variety of reasons,
> e.g. transient transport issue. And the resulting sequential scan can be
> extremely expensive on controllers reporting an NN value close to the
> maximum allowed (>4 billion). Avoid sequential scans wherever possible
> by only falling back to them if nvme_scan_ns_list fails due to
> controller non-support of Identify NS List.
Signed-off-by: Uday Shankar <ushankar@purestorage.com>
> ---
> This would break devices that claim to support version NVME_VS(1, 1, 0)
> or above, but don't support Identify NS List. But it looks like we
> already have NVME_QUIRK_IDENTIFY_CNS to deal with that.
>
> drivers/nvme/host/core.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 0090dc0b3ae6..5bd19819d33b 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -4535,7 +4535,7 @@ static void nvme_scan_work(struct work_struct *work)
> }
>
> mutex_lock(&ctrl->scan_lock);
> - if (nvme_scan_ns_list(ctrl) != 0)
> + if (nvme_scan_ns_list(ctrl) == -EOPNOTSUPP)
> nvme_scan_ns_sequential(ctrl);
> mutex_unlock(&ctrl->scan_lock);
> }
>
> base-commit: d30a909f9bb5283e701a5fdfffac763ef57a3e7c
> --
> 2.25.1
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] nvme: scan sequentially only when list scan unsupported
2022-11-04 22:36 [PATCH] nvme: scan sequentially only when list scan unsupported Uday Shankar
2022-11-04 22:46 ` Uday Shankar
@ 2022-11-07 5:56 ` Christoph Hellwig
2022-11-07 19:29 ` Uday Shankar
1 sibling, 1 reply; 4+ messages in thread
From: Christoph Hellwig @ 2022-11-07 5:56 UTC (permalink / raw)
To: Uday Shankar
Cc: linux-nvme, Christoph Hellwig, Keith Busch, Sagi Grimberg, Jens Axboe
On Fri, Nov 04, 2022 at 04:36:22PM -0600, Uday Shankar wrote:
> Currently, if nvme_scan_ns_list fails, nvme_scan_work will fall back to
> a sequential scan. nvme_scan_ns_list can fail for a variety of reasons,
> e.g. transient transport issue. And the resulting sequential scan can be
> extremely expensive on controllers reporting an NN value close to the
> maximum allowed (>4 billion). Avoid sequential scans wherever possible
> by only falling back to them if nvme_scan_ns_list fails due to
> controller non-support of Identify NS List.
> ---
> This would break devices that claim to support version NVME_VS(1, 1, 0)
> or above, but don't support Identify NS List. But it looks like we
> already have NVME_QUIRK_IDENTIFY_CNS to deal with that.
Yes. I'm a little worried about changing something this fundamental
after such a long time, even if it is the right thing to do. But at
least we get a warning when the Identify NS List fails, so between
that and the fact tht nvme_scan_ns_list logs an error I think we can
cope.
> mutex_lock(&ctrl->scan_lock);
> - if (nvme_scan_ns_list(ctrl) != 0)
> + if (nvme_scan_ns_list(ctrl) == -EOPNOTSUPP)
> nvme_scan_ns_sequential(ctrl);
Maybe make this a bit more clear by lifting the nvme_ctrl_limited_cns
check into nvme_scan_work, though:
if (nvme_ctrl_limited_cns(ctrl))
nvme_scan_ns_sequential(ctrl);
else
nvme_scan_ns_list(ctrl);
and drop the now superflous error return from nvme_scan_ns_list.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] nvme: scan sequentially only when list scan unsupported
2022-11-07 5:56 ` Christoph Hellwig
@ 2022-11-07 19:29 ` Uday Shankar
0 siblings, 0 replies; 4+ messages in thread
From: Uday Shankar @ 2022-11-07 19:29 UTC (permalink / raw)
To: Christoph Hellwig; +Cc: linux-nvme, Keith Busch, Sagi Grimberg, Jens Axboe
On Mon, Nov 07, 2022 at 06:56:05AM +0100, Christoph Hellwig wrote:
> Maybe make this a bit more clear by lifting the nvme_ctrl_limited_cns
> check into nvme_scan_work, though:
>
> if (nvme_ctrl_limited_cns(ctrl))
> nvme_scan_ns_sequential(ctrl);
> else
> nvme_scan_ns_list(ctrl);
>
> and drop the now superflous error return from nvme_scan_ns_list.
Sure. I will resubmit with that revision.
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2022-11-07 19:29 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2022-11-04 22:36 [PATCH] nvme: scan sequentially only when list scan unsupported Uday Shankar
2022-11-04 22:46 ` Uday Shankar
2022-11-07 5:56 ` Christoph Hellwig
2022-11-07 19:29 ` Uday Shankar
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