Re: MIPS: Add dependencies for HAVE_ARCH_TRANSPARENT_HUGEPAGE

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

On 03/20/2013 03:33 PM, Sebastian Gottschall wrote:
> Am 04.03.2013 05:17, schrieb Ben Hutchings:
>> The MIPS implementation of transparent huge-pages (THP) is 64-bit only,
>> and of course also requires that the CPU supports huge-pages.
>>
>> Currently it's entirely possible to enable THP in other configurations,
>> which then fail to build due to pfn_pmd() not being defined.
>>
>> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
>> Cc: David Daney <david.daney@cavium.com>
>> ---
>> --- a/arch/mips/Kconfig
>> +++ b/arch/mips/Kconfig
>> @@ -19,7 +19,7 @@ config MIPS
>>       select HAVE_KRETPROBES
>>       select HAVE_DEBUG_KMEMLEAK
>>       select ARCH_BINFMT_ELF_RANDOMIZE_PIE
>> -    select HAVE_ARCH_TRANSPARENT_HUGEPAGE
>> +    select HAVE_ARCH_TRANSPARENT_HUGEPAGE if CPU_SUPPORTS_HUGEPAGES
>> && 64BIT
>>       select RTC_LIB if !MACH_LOONGSON
>>       select GENERIC_ATOMIC64 if !64BIT
>>       select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
>>
> why? the mips32 74k platform (broadcom bcm4706 for instance) does
> support huge pages.

The hardware may support pages larger than 64K, but does the Linux 
kernel?  I think not.

> and some of these devices are also using highmem for
> accessing more than 128mb ram (which is totally broken in all current
> kernels too and causing filesystem corruptions)
> i was able to fix the highmem problem using a patch which was submitted
> but never taken into the mainline, but i just was able to get thb
> partially to work on mips32. but i think it would be possible to support
> this on mips32 as well. so why leaving it out?

As they say... Patches are welcome.  If you get Linux HUGE pages working 
for 32-bit kernels send a patch to enable the transparent variety as well.

David Daney