Re: [PATCH][RFC] mm: Introduce kernelcore=reliable option

[Kamezawa Hiroyuki]

On 2015/10/09 15:46, Xishi Qiu wrote:
> On 2015/10/9 22:56, Taku Izumi 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.
>
> Hi Taku,
>
> You mean set non-mirrored memory to movable zone, and set
> mirrored memory to normal zone, right? So kernel allocations
> will use mirrored memory in normal zone, and user allocations
> will use non-mirrored memory in movable zone.
>
> My question is:
> 1) do we need to change the fallback function?

For *our* requirement, it's not required. But if someone want to prevent
user's memory allocation from NORMAL_ZONE, we need some change in zonelist
walking.

> 2) the mirrored region should locate at the start of normal
> zone, right?

Precisely, "not-reliable" range of memory are handled by ZONE_MOVABLE.
This patch does only that.

> I remember Kame has already suggested this idea. In my opinion,
> I still think it's better to add a new migratetype or a new zone,
> so both user and kernel could use mirrored memory.

Hi, Xishi.

I and Izumi-san discussed the implementation much and found using "zone"
is better approach.

The biggest reason is that zone is a unit of vmscan and all statistics and
handling the range of memory for a purpose. We can reuse all vmscan and
information codes by making use of zones. Introdcing other structure will be messy.
His patch is very simple.

For your requirements. I and Izumi-san are discussing following plan.

 - Add a flag to show the zone is reliable or not, then, mark ZONE_MOVABLE as not-reliable.
 - Add __GFP_RELIABLE. This will allow alloc_pages() to skip not-reliable zone.
 - Add madivse() MADV_RELIABLE and modify page fault code's gfp flag with that flag.


Thanks,
-Kame





















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