linux-kernel - Re: [PATCH v3 0/5] dax: add PROBE_PREFER

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Message-ID: <691fb94f7aee9_1eb85100cd@dwillia2-mobl4.notmuch>
Date: Thu, 20 Nov 2025 16:58:55 -0800
From: <dan.j.williams@...el.com>
To: Michal Clapinski <mclapinski@...gle.com>, Dan Williams
	<dan.j.williams@...el.com>, Vishal Verma <vishal.l.verma@...el.com>, "Dave
 Jiang" <dave.jiang@...el.com>, <nvdimm@...ts.linux.dev>,
	<linux-cxl@...r.kernel.org>
CC: Pasha Tatashin <pasha.tatashin@...een.com>,
	<linux-kernel@...r.kernel.org>, Michal Clapinski <mclapinski@...gle.com>
Subject: Re: [PATCH v3 0/5] dax: add PROBE_PREFER_ASYNCHRONOUS to all the dax
 drivers

Michal Clapinski wrote:
> Comments in linux/device/driver.h say that the goal is to do async
> probing on all devices. The current behavior unnecessarily slows down
> the boot by synchronously probing dax devices, so let's change that.
> 
> For thousands of devices, this change saves >1s of boot time.
> 
> Michal Clapinski (5):
>   dax: add PROBE_PREFER_ASYNCHRONOUS to the pmem driver
>   dax: add PROBE_PREFER_ASYNCHRONOUS to the kmem driver
>   dax: add PROBE_PREFER_ASYNCHRONOUS to the cxl driver
>   dax: add PROBE_PREFER_ASYNCHRONOUS to the hmem drivers
>   dax: add PROBE_PREFER_ASYNCHRONOUS to the dax device driver

After seeing the trouble this causes with libdaxctl and failing to find
a quick fix I wonder if you should just go through route of eating the
potential regressions in your own environment.

I.e. instead of making it a problem that the kernel needs to debug for
all legacy users, how about you just boot with the command line option:

   driver_async_probe=device_dax

...or add the following to your mopdrobe configuration:

   options device_dax async_probe

I.e. do you really need to change this policy globally for everyone at
this point?

I do want to improve this, but I think it will take time for libdaxctl
to get ready for this flag day.