linux-kernel - Re: [PATCH v2 01/20] e820, efi: add ACPI 6.0 persistent memory types

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Date:	Tue, 28 Apr 2015 14:05:08 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	linux-nvdimm <linux-nvdimm@...ts.01.org>,
	Ingo Molnar <mingo@...nel.org>,
	Boaz Harrosh <boaz@...xistor.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...com>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>
Subject: Re: [PATCH v2 01/20] e820, efi: add ACPI 6.0 persistent memory types

On Tue, Apr 28, 2015 at 1:57 PM, Dan Williams <dan.j.williams@...el.com> wrote:
> On Tue, Apr 28, 2015 at 1:49 PM, Andy Lutomirski <luto@...capital.net> wrote:
>> On Tue, Apr 28, 2015 at 11:24 AM, Dan Williams <dan.j.williams@...el.com> wrote:
>>> diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
>>> index 11cc7d54ec3f..d38b53a7e9b2 100644
>>> --- a/arch/x86/kernel/e820.c
>>> +++ b/arch/x86/kernel/e820.c
>>> @@ -149,6 +149,7 @@ static void __init e820_print_type(u32 type)
>>>         case E820_UNUSABLE:
>>>                 printk(KERN_CONT "unusable");
>>>                 break;
>>> +       case E820_PMEM:
>>>         case E820_PRAM:
>>>                 printk(KERN_CONT "persistent (type %u)", type);
>>>                 break;
>>
>> I'd kind of like to make it more clear what's going on here.  It
>> doesn't help that the spec chose poor names.
>>
>> How about "NVDIMM physical aperture" for E820_PMEM and "legacy
>> persistent RAM" for E820_PRAM?
>
> The term "aperture" to me implies this BLK (mmio-windowed) mode of
> accessing persistent media that the NFIT specification introduces.  In
> fact, those ranges are mapped E820_RESERVED.  E820_PMEM really is a
> memory range that happens to be persistent.

Oh, I missed that.  Yuck.  What happens when you repartition one of
these things?  (Can you even do that?)

>
>> Otherwise this looks generaly sensible, although I don't really
>> understand why e820_type_to_string and e820_print_type are different.
>
>  e820_type_to_string() appears in /proc/iomem and seems to afford
> being more descriptive than e820_print_type() that just scrolls by in
> dmesg, but I'm just guessing.

Can we change that?

-- 
Andy Lutomirski
AMA Capital Management, LLC
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