Re: IP27: CONFIG_TRANSPARENT_HUGEPAGE triggers bus errors

[David Daney <ddaney.cavm@gmail.com>]

On 11/10/2014 09:03 AM, Ralf Baechle wrote:
> On Mon, Nov 10, 2014 at 08:55:09AM -0800, David Daney wrote:
>
>> Yes, you may be on to something here.  Certianly basic huge TLB support must
>> be in place for TRANSPARENT_HUGEPAGE to work.
>>
>> It could be that the Kconfig symbols for the various portions of huge page
>> support are missing the required dependencies.
>>
>> FWIW, I always build with a huge page Kconfig options set.
>>
>> I have:
>> $ grep HUGE .config
>> CONFIG_SYS_SUPPORTS_HUGETLBFS=y
>> CONFIG_MIPS_HUGE_TLB_SUPPORT=y
>> CONFIG_CPU_SUPPORTS_HUGEPAGES=y
>> CONFIG_TRANSPARENT_HUGEPAGE=y
>> CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS=y
>> # CONFIG_TRANSPARENT_HUGEPAGE_MADVISE is not set
>> CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE=y
>> CONFIG_HUGETLBFS=y
>> CONFIG_HUGETLB_PAGE=y
>>
>> I suspect that you may not need CONFIG_HUGETLBFS, but CONFIG_HUGETLB_PAGE is
>> probably essential.
>
> IP27 also has NUMA as the only in-tree MIPS system - and it's NUMA support
> is not in the best support state to say the least.  Just an observation -
> at this point in time there is no obvious connection between either
>
>    R10000 <-> transparent huge page
>
> or
>
>    NUMA <-> transparent huge page
>
>    Ralf
>

FYI, I am running with CONFIG_TRANSPARENT_HUGEPAGE on a 2-node NUMA 
system (48 CPUs per node) OCTEON III, and the huge pages have not been 
an issue.  So I don't think there are any inherent NUMA issues with 
HUGEPAGES.

David Daney