linux-kernel - Re: another pmem variant V2

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Date:	Thu, 26 Mar 2015 18:57:47 +0200
From:	Boaz Harrosh <boaz@...xistor.com>
To:	Christoph Hellwig <hch@....de>, linux-nvdimm@...1.01.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	x86@...nel.org
CC:	ross.zwisler@...ux.intel.com, axboe@...nel.dk, boaz@...xistor.com
Subject: Re: another pmem variant V2

On 03/26/2015 10:32 AM, Christoph Hellwig wrote:
> Here is another version of the same trivial pmem driver, because two
> obviously aren't enough.  The first patch is the same pmem driver
> that Ross posted a short time ago, just modified to use platform_devices
> to find the persistant memory region instead of hardconding it in the
> Kconfig.  This allows to keep pmem.c separate from any discovery mechanism,
> but still allow auto-discovery.
> 

Hi Christoph

So I've been trying to test your version, and play around with it.
I currently have some problems, but this is the end of the week for me
so I will debug and fix it after the weekend on Sunday.

But just a heads up for what I stumbled on.

For one this auto discovery of yours is very (very) nice but is a bit
inconvenience. Before I would reserve a big chuck on each NUMA range
on Kernel's memmap=  And then at pmem map= would slice and dice it
as I want hot style on modprobe with no need for reboot. Now I need
to do it on reboot theoretically. (You know xfstest needs lots of devices
some big some small ;-))

theoretically because if I try:
	memmap=1G!4G,1G!6G

It will not boot at all. (will debug on Sunday) I must have 2 devices
because each one is on another NUMA node.

If I do memmap=2G!4G,1G!6G , which is a contiguous range it will give
me only one device. Just an inconvenience. (And also this one sometimes
does not boot)

{All this in a VM for now did not even get to real HW yet}

Also with the modprob pmem map= I was supporting a PCIE memory card but
I guess I need to throw this one out the door.

Am also posting an RFC cleanup to your pmem driver. RFC because I was not
yet able to boot the all thing in our lab for heavy testing.

Thanks
Boaz

> The other two patches are a heavily rewritten version of the code that
> Intel gave to various storage vendors to discover the type 12 (and earlier
> type 6) nvdimms, which I massaged into a form that is hopefully suitable
> for mainline.
> 
> Note that pmem.c really is the minimal version as I think we need something
> included ASAP.  We'll eventually need to be able to do other I/O from and
> to it, and as most people know everyone has their own preferre method to
> do it, which I'd like to discuss once we have the basic driver in.
> 
> This has been tested both with a real NVDIMM on a system with a type 12
> capable bios, as well as with "fake persistent" memory using the memmap=
> option.
> 
> Changes since V1:
>   - s/E820_PROTECTED_KERN/E820_PMEM/g
>   - map the persistent memory as uncached
>   - better kernel parameter description
>   - various typo fixes
>   - MODULE_LICENSE fix
> 
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