Re: 1M hugepage size being registered on Linux

[victora <victora@linux.vnet.ibm.com>]

Em 2017-06-22 00:59, Michael Ellerman escreveu:
> Hi Victor,
> 
> Someone refreshed my memory on this, coffee was involved ...
> 
> victora <victora@linux.vnet.ibm.com> writes:
>> Hi Alistair/Jeremy,
>> 
>> I am working on a bug related to 1M hugepage size being registered on
>> Linux (Power 8 Baremetal - Garrison).
> 
> On those machines the property in the device tree comes straight from
> hostboot, and it includes 1M:
> 
> # lsprop ibm,segment-page-sizes
> ibm,segment-page-sizes
> 		 0000000c  00000000  00000003  0000000c
>                  baseshift slbenc    lpnum     shift
> 		 00000000  00000010  00000007  00000018
>                  penc      shift     penc      shift
> 		 00000038  00000010  00000110  00000002
>                  penc      baseshift slbenc    lpnum
> 		 00000010  00000001  00000018  00000008
>                  shift     penc      shift     penc
> 		 00000014  00000130  00000001  00000014	<--- 1MB = 2^0x14
>                  baseshift slbenc    lpnum     shift
> 		 00000002  00000018  00000100  00000001
>                  penc      baseshift slbenc    lpnum
> 		 00000018  00000000  00000022  00000120
>                  shift     penc      baseshift slbenc
> 		 00000001  00000022  00000003
>                  lpnum     shift     penc
> 
> 
>> I was checking dmesg and it seems that 1M page size is coming from
>> firmware to Linux.
>> 
>> [    0.000000] base_shift=20: shift=20, sllp=0x0130, avpnm=0x00000000, 
>> tlbiel=0, penc=2
>> [    1.528867] HugeTLB registered 1 MB page size, pre-allocated 0 
>> pages
> 
> Which is why you see that message.
> 
>> Should Linux support this page size? As afar as I know, this was an
>> unsupported page size in the past isn't it? If this should be 
>> supported
>> now, is there any specific reason for that?
> 
> It's unsupported in Linux because it doesn't match the page table
> geometry.
> 
> We merged a patch from Aneesh to filter it out in 4.12-rc1:
> 
>   a525108cf1cc ("powerpc/mm/hugetlb: Filter out hugepage size not
> supported by page table layout")
> 
> I guess we should probably send that patch to stable et. al.
> 
> cheers

Hi Michael,

Sorry for the delay. Thanks for merging that patch.
Was that patch also sent to stable et. al.?

Thanks
Victor