Re: IP27: CONFIG_TRANSPARENT_HUGEPAGE triggers bus errors

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

On 11/10/2014 06:22 AM, Joshua Kinard wrote:
> On 11/10/2014 06:20, Thomas Bogendoerfer wrote:
>> On Mon, Nov 10, 2014 at 11:51:06AM +0100, Ralf Baechle wrote:
>>> Thomas,
>>>
>>> can you test CONFIG_TRANSPARENT_HUGEPAGE on an IP28?
>>>
>>> All in all the R10000's TLB is unproblematic; my gut feeling is that
>>> rather something else specific to IP27 is spoiling the broth.
>>
>> I'll give it a spin later today.
>>
>> Thomas.
>
> Try testing with and without CONFIG_HUGETLBFS in the kernel.  File systems ->
> Pseudo filesystems -> HugeTLB file system support
>
> So far, it seems adding that option in with CONFIG_TRANSPARENT_HUGEPAGE makes
> both IP27 and IP30 behave.  Without, I get data bus errors or segfaults on IP27
> running Gentoo's "emerge" program on PAGE_SIZE_4K.
>
> IP30 seems to be fine on an R12000 with or without that option, but I only have
> a dual R12K module to test against.  I've only had the R14K dual module for a
> few days, and I could not reproduce the bus errors on that module, either.  So
> I wonder if there is something funny with the hardware on the single R14K
> module, which I did get IBE's on before.  And whether that will behave once
> CONFIG_HUGETLBFS is in the kernel.
>
> If so, maybe the fix is to make CONFIG_HUGETLBFS automatically selected if
> CONFIG_TRANSPARENT_HUGEPAGE?
>

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.



David Daney


> --J
>