linux-kernel - Re: [Linux-nvdimm] [PATCH 0/2] e820: Fix handling of NvDIMM chips

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Message-ID: <54EA0C48.4020408@plexistor.com>
Date:	Sun, 22 Feb 2015 19:05:12 +0200
From:	Boaz Harrosh <boaz@...xistor.com>
To:	Christoph Hellwig <hch@...radead.org>
CC:	Dan Williams <dan.j.williams@...el.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>, x86@...nel.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"Roger C. Pao" <rcpao.enmotus@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-nvdimm <linux-nvdimm@...1.01.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [Linux-nvdimm] [PATCH 0/2] e820: Fix handling of NvDIMM chips

On 02/22/2015 06:27 PM, Christoph Hellwig wrote:
> On Thu, Feb 19, 2015 at 11:25:37AM +0200, Boaz Harrosh wrote:
>> I do not see why you need the nvdimm_type= kernel option at all.
>>
>> I have here a script that auto detects any NvDIMM. It works with all
>> the chips that I have access to. And Also it has support for if you have
>> memmap=sss\$aaa.
>> For all these detected regions it will load a pmem device.
>>
>> It is easy to filter for any type of memory you want. What
>> will the (annoying) kernel option give you?
>>
>> OK I might be jumping the guns, send the patch and I'll look
>> at it.
> 
> The kernel option means we can autodetect the nvdimms in kernel space
> with just that option set, no need for needing userspace setup.
> 

Do you mean that pmem is:
- Loaded without any parameters.
- A new API is defined for enumerating NvDIMMs. pmem uses that for
  creating new devices.
- e820 registers such devices according to special type passed on Kernel
  command-line. (That could be a Kconfig as well you know, I hate Kernel
  command-line)

(Similar to what very old prd.c did only not hacking the e820 lists directly)

> How does your script / patch work?
> 

Easy just parses /proc/iomem + looks at Kernel command line.

It has support not only for type-12 memory but also for "reserved"
regions, made by memmap=sss$aaa stated on command line. And/or also
an /etc/pmem.cfg list of regions. So you can go automatic or manual or
a mix of both (And slice a region for xfstests scratch device).

In any case it helps to have my patches, but also old Kernels are
supported with the BLK_DEV_PMEM_IGNORE_REQUEST_MEM_RET. On old Kernels
they are all "reserved" regions, no unknown-12 type.

Once a list of regions or split-regions is established pmem is loaded
with that list.

> I won't be back to my nvdimm enabled hardware until after LSF/MM,
> so any work from me in this area will have to wait a bit.
> 

Have a good time. Will you guys have a talk about pmem ? If yes I
would love it if you guys can talk about the use-of-pages-with-pmem.
Please tell me I can write a looong argument about it.

Thanks
Boaz

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