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

[Mike Rapoport <rppt@kernel.org>]

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 :)

>  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
> 

-- 
Sincerely yours,
Mike.