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

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Message-ID: <CAAi7L5fMGANdMts8k4NGxJcWYsPmNwy4zJOXJ-t9T7h3h=mjOg@mail.gmail.com>
Date: Fri, 21 Nov 2025 17:33:05 +0100
From: Michał Cłapiński <mclapinski@...gle.com>
To: dan.j.williams@...el.com
Cc: Vishal Verma <vishal.l.verma@...el.com>, Dave Jiang <dave.jiang@...el.com>, 
	nvdimm@...ts.linux.dev, linux-cxl@...r.kernel.org, 
	Pasha Tatashin <pasha.tatashin@...een.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/5] dax: add PROBE_PREFER_ASYNCHRONOUS to all the dax drivers

On Fri, Nov 21, 2025 at 1:59 AM <dan.j.williams@...el.com> wrote:
>
> 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'll do that or I'll just cherry-pick this to our kernel. Thank you.

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