ARM: fix bug which lowmem size is limited to 760MB

Message ID alpine.LFD.2.20.1509071128151.22877@knanqh.ubzr
State New
Headers show

Commit Message

Nicolas Pitre Sept. 7, 2015, 3:34 p.m.
On Mon, 7 Sep 2015, Arnd Bergmann wrote:

> Given how much more common 1GB hardware configurations are compared to 768MB
> configuration, we could however think about adding a VMSPLIT_3G_OPT option
> that x86 has (also VMSPLIT_2_75G on ARCH_TILE), to allow using the entire
> 1GB of lowmem without going all the way to VMSPLIT_2G. That option would
> also let us use the entire 768MB on the machines that 	Yongtaek Lee is
> interested in.

That's easy enough:



That shifts the risk to user space though.  But if there is a regression 
there, it will manifest itself on all systems and not only with some 
particular hardware.


Nicolas
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Comments

Arnd Bergmann Sept. 7, 2015, 3:45 p.m. | #1
On Monday 07 September 2015 11:34:36 Nicolas Pitre wrote:
> 
> That shifts the risk to user space though.  But if there is a regression 
> there, it will manifest itself on all systems and not only with some 
> particular hardware.

I'd consider that a good thing, as it makes it easier to test when
you see the same behavior on systems with any memory size.

	Arnd
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Nicolas Pitre Sept. 7, 2015, 3:49 p.m. | #2
On Mon, 7 Sep 2015, Arnd Bergmann wrote:

> On Monday 07 September 2015 11:34:36 Nicolas Pitre wrote:
> > 
> > That shifts the risk to user space though.  But if there is a regression 
> > there, it will manifest itself on all systems and not only with some 
> > particular hardware.
> 
> I'd consider that a good thing, as it makes it easier to test when
> you see the same behavior on systems with any memory size.

Sure, that was my point, although I admitedly didn't say it clearly.


Nicolas
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Patch

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 0d1b717e1e..a63970f211 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1470,6 +1470,8 @@  choice
 
 	config VMSPLIT_3G
 		bool "3G/1G user/kernel split"
+	config VMSPLIT_3G_OPT
+		bool "3G/1G user/kernel split (for full 1G low memory)"
 	config VMSPLIT_2G
 		bool "2G/2G user/kernel split"
 	config VMSPLIT_1G
@@ -1481,6 +1483,7 @@  config PAGE_OFFSET
 	default PHYS_OFFSET if !MMU
 	default 0x40000000 if VMSPLIT_1G
 	default 0x80000000 if VMSPLIT_2G
+	default 0xAF000000 if VMSPLIT_3G_OPT
 	default 0xC0000000
 
 config NR_CPUS