Re: [RFC PATCH 10/12] mm: add the buddy system interface

[Kamezawa Hiroyuki]

On 2015/06/11 5:40, Luck, Tony wrote:
> > I guess, mirrored memory should be allocated if !__GFP_HIGHMEM or !__GFP_MOVABLE
>
> HIGHMEM shouldn't matter - partial memory mirror only makes any sense on X86_64 systems ... 32-bit kernels
> don't even boot on systems with 64GB, and the minimum rational configuration for a machine that supports
> mirror is 128GB (4 cpu sockets * 2 memory controller per socket * 4 channels per controller * 4GB DIMM ...
> leaving any channels empty likely leaves you short of memory bandwidth for these high core count processors).
>
> MOVABLE is mostly the opposite of MIRROR - we never want to fill a kernel allocation from a MOVABLE page. I
> want all kernel allocations to be from MIRROR.

So, there are 3 ideas.

 (1) kernel only from MIRROR / user only from MOVABLE (Tony)
 (2) kernel only from MIRROR / user from MOVABLE + MIRROR(ASAP)  (AKPM suggested)
     This makes use of the fact MOVABLE memory is reclaimable but Tony pointed out
     the memory reclaim can be critical for GFP_ATOMIC.
 (3) kernel only from MIRROR / user from MOVABLE, special user from MIRROR (Xishi)

2 Implementation ideas.
  - creating ZONE
  - creating new alloation attribute

I don't convince whether we need some new structure in mm. Isn't it good to use
ZONE_MOVABLE for not-mirrored memory ?
Then, disable fallback from ZONE_MOVABLE -> ZONE_NORMAL for (1) and (3)

Thanks,
-Kame


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