linux-kernel - Re: [RFC PATCH 00/20] Introduce the famfs shared-memory file system

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Message-ID: <ZlJsNir3mBUK0Ofb@dread.disaster.area>
Date: Sun, 26 May 2024 08:54:46 +1000
From: Dave Chinner <david@...morbit.com>
To: Miklos Szeredi <miklos@...redi.hu>
Cc: John Groves <John@...ves.net>, linux-cxl@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	nvdimm@...ts.linux.dev
Subject: Re: [RFC PATCH 00/20] Introduce the famfs shared-memory file system

On Fri, May 24, 2024 at 09:55:48AM +0200, Miklos Szeredi wrote:
> On Fri, 24 May 2024 at 02:47, John Groves <John@...ves.net> wrote:
> 
> > Apologies, but I'm short on time at the moment - going into a long holiday
> > weekend in the US with family plans. I should be focused again by middle of
> > next week.
> 
> NP.
> 
> Obviously I'll need to test it before anything is merged, other than
> that this is not urgent at all...
> 
> > But can you check /proc/cmdline to see of the memmap arg got through without
> > getting mangled? The '$' tends to get fubar'd. You might need \$, or I've seen
> > the need for \\\$. If it's un-mangled, there should be a dax device.
> 
> /proc/cmdline shows the option correctly:
> 
> root@kvm:~# cat /proc/cmdline
> root=/dev/vda console=hvc0 memmap=4G$4G
> 
> > If that doesn't work, it's worth trying '!' instead, which I think would give
> > you a pmem device - if the arg gets through (but ! is less likely to get
> > horked). That pmem device can be converted to devdax...
> 
> That doesn't work either.  No device created in /dev  (dax or pmem).

I think you need to do some ndctl magic to get the memory to be
namespaced correctly for the correct devices to appear.

https://docs.pmem.io/ndctl-user-guide/managing-namespaces

IIRC, need to set the type to pmem and the mode to fsdax, devdax or
raw to get the relevant device nodes to be created for the range..

Cheers,

Dave.

-- 
Dave Chinner
david@...morbit.com