THP broken on MIPS-32 [3.8]

THP broken on MIPS-32 [3.8]

[Ben Hutchings]

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You implemented transparent huge pages for MIPS:

commit 970d032fec3f9687446595ee2569fb70b858a69f
Author: Ralf Baechle <ralf@linux-mips.org>
Date:   Thu Oct 18 13:54:15 2012 +0200

    MIPS: Transparent Huge Pages support

but THP also changed in 3.8:

commit fc9fe822f7112db23e51e2be3b886f5d8f0afdb6
Author: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Date:   Wed Dec 12 13:50:51 2012 -0800

    thp: copy_huge_pmd(): copy huge zero page

This added the requirement for pfn_pmd(), which is only defined if
CONFIG_64BIT && !CONFIG_CPU_VR41XX.

Ben.

-- 
Ben Hutchings
Computers are not intelligent.	They only think they are.

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MIPS: Add dependencies for HAVE_ARCH_TRANSPARENT_HUGEPAGE

[Ben Hutchings]

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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


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Re: MIPS: Add dependencies for HAVE_ARCH_TRANSPARENT_HUGEPAGE

[David Daney]

On 03/03/2013 08:17 PM, Ben Hutchings wrote:
> 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>

This is correct.

Acked-by: 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
>

Re: MIPS: Add dependencies for HAVE_ARCH_TRANSPARENT_HUGEPAGE

[Ralf Baechle]

Thanks, applied.

  Ralf

Re: MIPS: Add dependencies for HAVE_ARCH_TRANSPARENT_HUGEPAGE

[Sebastian Gottschall]

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. 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?

regards,
Sebastian Gottschall

Re: MIPS: Add dependencies for HAVE_ARCH_TRANSPARENT_HUGEPAGE

[David Daney]

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

Re: MIPS: Add dependencies for HAVE_ARCH_TRANSPARENT_HUGEPAGE

[Sebastian Gottschall]

>> 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

the first patch would be fix for the HIGHMEM problem. all recent kernels 
do support HIGHMEM for mips32 based devices, but in fact its not 
working. all patches i made which is required to get it to work is 
available at svn://svn.dd-wrt.com/DD-WRT for all recent kernels.

for mips32 HIGHMEM support you need to apply the following patch

http://patchwork.linux-mips.org/patch/3634/

this patch has a small typo, which needs to be fixed but its very easy 
to merge to all current kernels. without it, highmem enabled devices 
will cause memory corruptions. especially on filesystems wrong data will 
be written and so on.

i will try to test my older thb patch with the new highmem fixes 
together next and i hope it works. in the meantime, please review the 
patchlink above

Sebastian