On 12/3/21 3:02 PM, Dennis Zhou wrote:

On Wed, Dec 01, 2021 at 11:51:04AM +0000, Vladimir Murzin wrote:

quoted

Hi,

On 11/30/21 5:41 PM, Dennis Zhou wrote:

quoted

Hello,

On Tue, Nov 30, 2021 at 05:29:54PM +0000, Vladimir Murzin wrote:

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Currently, NOMMU pull km allocator via !SMP dependency because most of
them are UP, yet for SMP+NOMMU vm allocator gets pulled which:

* may lead to broken build [1]
* ...or not working runtime due to [2]

It looks like SMP+NOMMU case was overlooked in bbddff054587 ("percpu:
use percpu allocator on UP too") so restore that.

[1]
For ARM SMP+NOMMU (R-class cores)

arm-none-linux-gnueabihf-ld: mm/percpu.o: in function `pcpu_post_unmap_tlb_flush':
mm/percpu-vm.c:188: undefined reference to `flush_tlb_kernel_range'

[2]
static inline
int vmap_pages_range_noflush(unsigned long addr, unsigned long end,
                pgprot_t prot, struct page **pages, unsigned int page_shift)
{
       return -EINVAL;
}

Signed-off-by: Vladimir Murzin <redacted>
---
 mm/Kconfig | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/Kconfig b/mm/Kconfig
index d16ba92..66331e0 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig

@@ -425,9 +425,8 @@ config THP_SWAP
 # UP and nommu archs use km based percpu allocator
 #
 config NEED_PER_CPU_KM
-	depends on !SMP
 	bool
-	default y
+	default !SMP || !MMU
 

Should this be `depends on !SMP || !MMU` with default yes? Because with
SMP && MMU, it shouldn't be an option to run with percpu-km.

IIUC these are equivalent, truth table would not change if is under "depends"
or "default"

SMP    MMU   NEED_PER_CPU_KM
 y      y    !y || !y => n || n => n
 y      n    !y || !n => n || y => y
 n      y    !n || !y => y || n => y
 n      n    !n || !n => y || y => y

I may be wrong, but I think this is slightly different as we're using
#ifdef / #if defined().

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 config CLEANCACHE
 	bool "Enable cleancache driver to cache clean pages if tmem is present"
-- 
2.7.4

It's interesting to me that this is all coming up at once. Earlier this
month I had the same conversation with people involved with sh [1].

[1] https://lore.kernel.org/linux-sh/YY7tp5attRyK42Zk@fedora/ (local)

I can pull this shortly once I see whatever happened to linux-sh.

Ahh, good to know! Adding SH folks here (start of discussion [0]). I see you came
to the same conclusion, right? 

Yeah, I don't see anything else from linux-sh. So I'll go ahead and
apply this with my change if you're fine with that.

I can't test against current until I get some unrelated fixes from Rich Felker
(who's been busy over the weekend), but I tested the "depends" version on 5.10
and got a shell prompt on my "make ARCH=sh j2_defconfig" board.

Tested-by: Rob Landley <redacted>

Rob