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Subject: Re: [PATCH V2 1/2] mm: move FAULT_AROUND_ORDER to arch/
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Dave Hansen <dave.hansen@intel.com>
Date: Mon, 07 Apr 2014 15:45:34 +1000
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Cc: linux-arch@vger.kernel.org, rusty@rustcorp.com.au,
 Madhavan Srinivasan <maddy@linux.vnet.ibm.com>, riel@redhat.com,
 x86@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org,
 peterz@infradead.org, ak@linux.intel.com, paulus@samba.org, mgorman@suse.de,
 akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org, mingo@kernel.org,
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On Fri, 2014-04-04 at 09:18 -0700, Dave Hansen wrote:
> On 04/03/2014 11:27 PM, Madhavan Srinivasan wrote:
> > This patch creates infrastructure to move the FAULT_AROUND_ORDER
> > to arch/ using Kconfig. This will enable architecture maintainers
> > to decide on suitable FAULT_AROUND_ORDER value based on
> > performance data for that architecture. Patch also adds
> > FAULT_AROUND_ORDER Kconfig element in arch/X86.
> 
> Please don't do it this way.
> 
> In mm/Kconfig, put
> 
> 	config FAULT_AROUND_ORDER
> 		int
> 		default 1234 if POWERPC
> 		default 4
> 
> The way you have it now, every single architecture that needs to enable
> this has to go put that in their Kconfig.  That's madness.  This way,
> you only put it in one place, and folks only have to care if they want
> to change the default to be something other than 4.

Also does it have to be a constant ? Maddy here tested on our POWER
servers. The "Sweet spot" value might be VERY different on an embedded
chip or even on a future generation of server chip.

Cheers,
Ben.