On Tue, 25 May 2021 08:40:10 PDT (-0700), rdunlap@infradead.org wrote:

On 5/25/21 3:33 AM, Mike Rapoport wrote:

quoted

On Mon, May 24, 2021 at 05:13:02PM -0700, Randy Dunlap wrote:

quoted

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 <redacted>
Cc: Paul Walmsley <redacted>
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 <redacted>

Acked-by: Mike Rapoport <redacted>

quoted

---
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.

IMO 15626062f4a9 ("thp, x86: introduce HAVE_ARCH_TRANSPARENT_HUGEPAGE") 
is really saying "the arches that have transparent huge pages are MMU=y, 
so we don't need the extra check".  That seems reasonable as of when the 
code landed, and while arm has MMU=n and THP it already depends on MMU 
(via ARM_LPAE, which seems kind of natural there).

The generic version seems fine to me, but I'm going to take this one now 
so we can avoid the build issues.

quoted

quoted

 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.