linux-kernel - Re: another pmem variant V2

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Date:	Tue, 31 Mar 2015 13:25:46 +0300
From:	Boaz Harrosh <boaz@...xistor.com>
To:	Christoph Hellwig <hch@....de>, Boaz Harrosh <boaz@...xistor.com>
CC:	linux-nvdimm@...1.01.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	ross.zwisler@...ux.intel.com, axboe@...nel.dk
Subject: Re: another pmem variant V2

On 03/31/2015 12:25 PM, Christoph Hellwig wrote:
> On Thu, Mar 26, 2015 at 06:57:47PM +0200, Boaz Harrosh wrote:
>> 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.
> 
> Any news?  I'd really like to resend this ASAP to get it into 4.1..

Yes sorry I got stuck with the NUMA thing. I will finally finish today.

For some reason your patch with the memmap=nn!aa behaves differently than
with  memmap=nn\$aa

And also compared to my old e820.c fix + my old pmem. My fixes are effectively
the same as with your Kernel and the memmap=nn\$aa which sets the range "reserved"
like. And less "ram" like as in your patch.

The problem I see is that if I state a memmap=nn!aa that crosses a NUMA
boundary then the machine will not boot.
So BTW for sure I need that "don't merge E820_PMEM ranges" patch because
otherwise I will not be able to boot if I have pmem on both NUMA nodes
and they happen to be contiguous.

I do not understand why this happens, because a contiguous range of
RAM is fine with cross NUMA and pmem not. (Also the pmem defined as
memmap=nn!aa behaves the same)

Also we have another problem with NUMA that I'm researching for a solution
long term. Is that if the second NUMA node has only pmem and no RAM than
the Kernel will not define a second NUMA node. And we are NUMA screwed with
pmem. So one must put v-ram and nv-ram equally spread across his nodes.

Regarding the SQUASHMEs to PMEM. Originally I had them as 3-4 patches.
But I thought since you are squashing them into a single submitted patch
I can just send just the one patch. Tell me what you prefer and I'll
resend (The one vs the three)

And one last issue. I have some configuration "hardness" with the
memmap=nn!aa Kernel command line API, it was better for me with the
pmem map= module param. Will you be OK if I split pmem_probe() into
calling pmem_alloc(addr, length), so I can keep an out-of-tree patch
that adds the map= parameter to pmem?

Will send the patch in one hour. Just tell me if you need just the one
or three.

Thanks, Christoph
Boaz

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