linux-kernel - Re: [PATCH 2/2] x86: Add "make tinyconfig" to configure the tiniest possible kernel

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Date:	Thu, 7 Aug 2014 12:02:44 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	David Rientjes <rientjes@...gle.com>,
	"Luis R. Rodriguez" <mcgrof@...e.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] x86: Add "make tinyconfig" to configure the tiniest
 possible kernel

On Thu, Aug 07, 2014 at 06:03:52PM +0200, Sam Ravnborg wrote:
> On Wed, Aug 06, 2014 at 03:31:54PM -0700, Josh Triplett wrote:
> > Since commit 5d2acfc7b974bbd3858b4dd3f2cdc6362dd8843a ("kconfig: make
> > allnoconfig disable options behind EMBEDDED and EXPERT") in 3.15-rc1,
> > "make allnoconfig" disables every possible config option.
> > 
> > However, a few configuration options (CC_OPTIMIZE_FOR_SIZE,
> > OPTIMIZE_INLINING) produce a smaller kernel when turned on, and a few
> > choices exist (compression, highmem, allocator) for which a non-default
> > option produces a smaller kernel.
> > 
> > Add a "tinyconfig" option, which starts from allnoconfig and then sets
> > these options to configure the tiniest possible kernel.  This provides a
> > better baseline for embedded systems or efforts to reduce kernel size.
> 
> In general I dislike the whole approach where we introduce makefile
> magic to support diverse config snippets.
> Another approch where we factor out this from the MAkefile seems much leaner.
> 
> And for this specific patch then this is not x86 specific at all.
> If we keep the logic in the makefiles than we should:
> 1) Make the infrastructure general
> 2) Document it
> 3) Find another home for the config snippets that are non-arch specific like this one

I'll refactor this and resubmit.

> > diff --git a/arch/x86/configs/tiny.config b/arch/x86/configs/tiny.config
> > new file mode 100644
> > index 0000000..8f0e54c
> > --- /dev/null
> > +++ b/arch/x86/configs/tiny.config
> > @@ -0,0 +1,5 @@
> > +CONFIG_CC_OPTIMIZE_FOR_SIZE=y
> > +CONFIG_KERNEL_XZ=y
> > +CONFIG_NOHIGHMEM=y
> > +CONFIG_OPTIMIZE_INLINING=y
> > +CONFIG_SLOB=y
> All the above are general options that apply equal to arm than to x86.

NOHIGHMEM isn't.

- Josh Triplett
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