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Re: [PATCH v2 0/2] mm: Introduce kernelcore=reliable option

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  Re: [PATCH v2 0/2] mm: Introduce kernelcore=reliable option Andrew Morton <akpm@linux-foundation.org> - 2015-12-08 01:40 +0100
    RE: [PATCH v2 0/2] mm: Introduce kernelcore=reliable option "Izumi, Taku" <izumi.taku@jp.fujitsu.com> - 2015-12-08 09:10 +0100
      Re: [PATCH v2 0/2] mm: Introduce kernelcore=reliable option Tony Luck <tony.luck@gmail.com> - 2015-12-08 17:20 +0100
        RE: [PATCH v2 0/2] mm: Introduce kernelcore=reliable option "Izumi, Taku" <izumi.taku@jp.fujitsu.com> - 2015-12-09 01:00 +0100

#1286128 — Re: [PATCH v2 0/2] mm: Introduce kernelcore=reliable option

On Sat, 28 Nov 2015 00:03:55 +0900 Taku Izumi <izumi.taku@jp.fujitsu.com> wrote:

> Xeon E7 v3 based systems supports Address Range Mirroring
> and UEFI BIOS complied with UEFI spec 2.5 can notify which
> ranges are reliable (mirrored) via EFI memory map.
> Now Linux kernel utilize its information and allocates
> boot time memory from reliable region.
> 
> My requirement is:
>   - allocate kernel memory from reliable region
>   - allocate user memory from non-reliable region
> 
> In order to meet my requirement, ZONE_MOVABLE is useful.
> By arranging non-reliable range into ZONE_MOVABLE,
> reliable memory is only used for kernel allocations.
> 
> My idea is to extend existing "kernelcore" option and
> introduces kernelcore=reliable option. By specifying
> "reliable" instead of specifying the amount of memory,
> non-reliable region will be arranged into ZONE_MOVABLE.

It is unfortunate that the kernel presently refers to this memory as
"mirrored", but this patchset introduces the new term "reliable".  I
think it would be better if we use "mirrored" throughout.

Of course, mirroring isn't the only way to get reliable memory. 
Perhaps if a part of the system memory has ECC correction then this
also can be accessed using "reliable", in which case your proposed
naming makes sense.  reliable == mirrored || ecc?



Secondly, does this patchset mean that kernelcore=reliable and
kernelcore=100M are exclusive?  Or can the user specify
"kernelcore=reliable,kernelcore=100M" to use 100M of reliable memory
for kernelcore?

This is unclear from the documentation and I suggest that this be
spelled out.

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#1286300

Dear Tony,

  Thanks for testing!

Dear Andrew,


> > Xeon E7 v3 based systems supports Address Range Mirroring
> > and UEFI BIOS complied with UEFI spec 2.5 can notify which
> > ranges are reliable (mirrored) via EFI memory map.
> > Now Linux kernel utilize its information and allocates
> > boot time memory from reliable region.
> >
> > My requirement is:
> >   - allocate kernel memory from reliable region
> >   - allocate user memory from non-reliable region
> >
> > In order to meet my requirement, ZONE_MOVABLE is useful.
> > By arranging non-reliable range into ZONE_MOVABLE,
> > reliable memory is only used for kernel allocations.
> >
> > My idea is to extend existing "kernelcore" option and
> > introduces kernelcore=reliable option. By specifying
> > "reliable" instead of specifying the amount of memory,
> > non-reliable region will be arranged into ZONE_MOVABLE.
> 
> It is unfortunate that the kernel presently refers to this memory as
> "mirrored", but this patchset introduces the new term "reliable".  I
> think it would be better if we use "mirrored" throughout.
> Of course, mirroring isn't the only way to get reliable memory.

  YES. "mirroring" is not the only way.
  So, in my opinion, we should change "mirrored" into "reliable" in order
  to match terms of UEFI 2.5 spec.

> Perhaps if a part of the system memory has ECC correction then this
> also can be accessed using "reliable", in which case your proposed
> naming makes sense.  reliable == mirrored || ecc?

  "reliable" is better.

  But, I'm willing to change "reliable" into "mirrored".

  Otherwise, I keep "kernelcore=reliable" and add the following minimal fix as 
  a separate patch:

diff  a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
--- a/arch/x86/platform/efi/efi.c
+++ b/arch/x86/platform/efi/efi.c
@@ -134,7 +134,7 @@ void __init efi_find_mirror(void)
                }
        }
        if (mirror_size)
-               pr_info("Memory: %lldM/%lldM mirrored memory\n",
+               pr_info("Memory: %lldM/%lldM reliable memory\n",
                        mirror_size>>20, total_size>>20);
 }

 
 Which do you think is beter ?
   - change into kernelcore="mirrored"
   - keep kernelcore="reliable" and minmal printk fix 

> 
> Secondly, does this patchset mean that kernelcore=reliable and
> kernelcore=100M are exclusive?  Or can the user specify
> "kernelcore=reliable,kernelcore=100M" to use 100M of reliable memory
> for kernelcore?

  No, these are exclusive.
> 
> This is unclear from the documentation and I suggest that this be
> spelled out.

  Thanks. I'll update its document.

 Sincerely,
 Taku Izumi
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#1286647

On Tue, Dec 8, 2015 at 12:07 AM, Izumi, Taku <izumi.taku@jp.fujitsu.com> wrote:
>  Which do you think is beter ?
>    - change into kernelcore="mirrored"
>    - keep kernelcore="reliable" and minmal printk fix

UEFI came up with the "reliable" wording (as a more generic term ...
as Andrew said
it could cover differences in ECC modes, or some alternate memory
technology that
has lower error rates).

But I personally like "mirror" more ... it matches current
implementation. Of course
I'll look silly if some future system does something other than mirror.

-Tony
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#1286921

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