Re: [PATCH -next] riscv: TRANSPARENT_HUGEPAGE: depends on MMU

[Randy Dunlap <rdunlap@infradead.org>]

On 5/25/21 3:33 AM, Mike Rapoport wrote:
> On Mon, May 24, 2021 at 05:13:02PM -0700, Randy Dunlap wrote:
>> Fix a Kconfig warning and many build errors:
>>
>> WARNING: unmet direct dependencies detected for COMPACTION
>>   Depends on [n]: MMU [=n]
>>   Selected by [y]:
>>   - TRANSPARENT_HUGEPAGE [=y] && HAVE_ARCH_TRANSPARENT_HUGEPAGE [=y]
>>
>> and the subseqent thousands of build errors and warnings.
>>
>> Fixes: e88b333142e4 ("riscv: mm: add THP support on 64-bit")
>> Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
>> Cc: Paul Walmsley <paul.walmsley@sifive.com>
>> Cc: Palmer Dabbelt <palmer@dabbelt.com>
>> Cc: Albert Ou <aou@eecs.berkeley.edu>
>> Cc: linux-riscv@lists.infradead.org
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Nanyong Sun <sunnanyong@huawei.com>
> 
> Acked-by: Mike Rapoport <rppt@linux.ibm.com>
> 
>> ---
>> I really think that mm/Kconfig should have "depends on MMU" for
>> TRANSPARENT_HUGEPAGE, but commit 15626062f4a9 from 2012
>> ("thp, x86: introduce HAVE_ARCH_TRANSPARENT_HUGEPAGE") thought
>> differently. I.e., mm/Kconfig should be protecting all arches
>> against this Kconfig problem.
> 
> We could 
> 
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 02d44e3420f5..85bc8bf32e7b 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -403,7 +403,7 @@ config NOMMU_INITIAL_TRIM_EXCESS
>  
>  config TRANSPARENT_HUGEPAGE
>  	bool "Transparent Hugepage Support"
> -	depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE
> +	depends on MMU && HAVE_ARCH_TRANSPARENT_HUGEPAGE
>  	select COMPACTION
>  	select XARRAY_MULTI
>  	help
> 
> but in a sense HAVE_ARCH_TRANSPARENT_HUGEPAGE should imply that MMU is
> selected :)

Yes, I had this patch before the one that I sent but decided against it
based on history.

>>  arch/riscv/Kconfig |    2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> --- linux-next-20210524.orig/arch/riscv/Kconfig
>> +++ linux-next-20210524/arch/riscv/Kconfig
>> @@ -106,7 +106,7 @@ config RISCV
>>  	select SYSCTL_EXCEPTION_TRACE
>>  	select THREAD_INFO_IN_TASK
>>  	select UACCESS_MEMCPY if !MMU
>> -	select HAVE_ARCH_TRANSPARENT_HUGEPAGE if 64BIT
>> +	select HAVE_ARCH_TRANSPARENT_HUGEPAGE if 64BIT && MMU
>>  
>>  config ARCH_MMAP_RND_BITS_MIN
>>  	default 18 if 64BIT
>>
> 

thanks.
-- 
~Randy