Re: [PATCH v2 1/3] ARM: Make FORCE_MAX_ZONEORDER configurable if ARM_SINGLE_ARMV7M

From: Uwe Kleine-König
Date: Thu Sep 10 2015 - 03:54:23 EST

On Wed, Sep 09, 2015 at 07:41:25AM +0200, Uwe Kleine-König wrote:
> On Tue, Sep 08, 2015 at 11:19:13PM +0100, Russell King - ARM Linux wrote:
> > On Tue, Sep 08, 2015 at 10:38:04PM +0200, Maxime Coquelin wrote:
> > > This patch makes FORCE_MAX_ZONEORDER configurable in defconfig for ARMV7-M
> > > when built for a single platform.
> >
> > I'd prefer if we didn't do this, because this isn't supposed to be a user
> > visible "option". It's an option that was introduced to avoid having to
> > throw masses of #ifdefs into the definition of MAX_ZONEORDER.
> >
> > The problem with it is that it's a "well, what do I set this to?" option
> > and that leads to "oh, I'll just choose the default because I don't know
> > any better".
> >
> > Do we know why EFM32 needs a value of 9 here? It's not documented in
> > the original commit, and it really _should_ have been.
> IIRC it was done because of memory pressure. But not sure this makes any
> sense. I will try with the default value later today and report back.
I updated my patch stack to 4.2 and the difference between 9 and 11 is:

Using 9:

/ # free
total used free shared buffers
Mem: 3744 1688 2056 0 0
-/+ buffers: 1688 2056

vs. using 11:

/ # free
total used free shared buffers
Mem: 3744 1696 2048 0 0
-/+ buffers: 1696 2048

so it works with bearable costs. If you want to get rid of the special
casing for efm32 that's fine for me.

Best regards
Uwe

--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
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