linux-kernel - Re: [PATCH] MIPS: Increase range of CONFIG_FORCE_MAX

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Message-Id: <O3L2HQ.37Y7OUPZFQDO1@crapouillou.net>
Date:   Tue, 22 Sep 2020 19:11:48 +0200
From:   Paul Cercueil <paul@...pouillou.net>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc:     od@...c.me, linux-mips@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] MIPS: Increase range of CONFIG_FORCE_MAX_ZONEORDER

Hi Thomas,

Le mar. 22 sept. 2020 à 18:02, Thomas Bogendoerfer 
<tsbogend@...ha.franken.de> a écrit :
> On Thu, Sep 17, 2020 at 03:35:28PM +0200, Paul Cercueil wrote:
>>  There is nothing that prevents us from using lower maximum values.
>>  It's something that we actually want, when using bigger page sizes 
>> on
>>  devices with low RAM.
>> 
>>  Signed-off-by: Paul Cercueil <paul@...pouillou.net>
>>  ---
>>   arch/mips/Kconfig | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>>  diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
>>  index 632fe8fe68c4..dca2bbdbfc24 100644
>>  --- a/arch/mips/Kconfig
>>  +++ b/arch/mips/Kconfig
>>  @@ -2251,7 +2251,7 @@ config FORCE_MAX_ZONEORDER
>>   	default "13" if MIPS_HUGE_TLB_SUPPORT && PAGE_SIZE_32KB
>>   	range 12 64 if MIPS_HUGE_TLB_SUPPORT && PAGE_SIZE_16KB
>>   	default "12" if MIPS_HUGE_TLB_SUPPORT && PAGE_SIZE_16KB
>>  -	range 11 64
>>  +	range 0 64
> 
> Do we need the range at all ? Most other archs don't use a range...

The maximum contiguous block size cannot be lower than a huge page, so 
that's why the 'range' are here.

Which makes me think that there should probably be a "range 11 64 if 
MIPS_HUGE_TLB_SUPPORT && PAGE_SIZE_8KB" and the same for 4KB pages.

With a lower value and huge pages enabled in the config, the kernel 
probably would not boot.

Cheers,
-Paul