linux-kernel - Re: [PATCH V4 0/2] mm: FAULT_AROUND_ORDER patchset performance data for powerpc

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Message-ID: <alpine.LSU.2.11.1405151026540.4664@eggly.anvils>
Date:	Thu, 15 May 2014 10:28:17 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>
cc:	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	linux-mm@...ck.org, linux-arch@...r.kernel.org, x86@...nel.org,
	benh@...nel.crashing.org, paulus@...ba.org,
	kirill.shutemov@...ux.intel.com, rusty@...tcorp.com.au,
	akpm@...ux-foundation.org, riel@...hat.com, mgorman@...e.de,
	ak@...ux.intel.com, peterz@...radead.org, mingo@...nel.org,
	dave.hansen@...el.com
Subject: Re: [PATCH V4 0/2] mm: FAULT_AROUND_ORDER patchset performance data
 for powerpc

On Thu, 15 May 2014, Madhavan Srinivasan wrote:
> 
> Hi Ingo,
> 
> 	Do you have any comments for the latest version of the patchset. If
> not, kindly can you pick it up as is.
> 
> 
> With regards
> Maddy
> 
> > Kirill A. Shutemov with 8c6e50b029 commit introduced
> > vm_ops->map_pages() for mapping easy accessible pages around
> > fault address in hope to reduce number of minor page faults.
> > 
> > This patch creates infrastructure to modify the FAULT_AROUND_ORDER
> > value using mm/Kconfig. This will enable architecture maintainers
> > to decide on suitable FAULT_AROUND_ORDER value based on
> > performance data for that architecture. First patch also defaults
> > FAULT_AROUND_ORDER Kconfig element to 4. Second patch list
> > out the performance numbers for powerpc (platform pseries) and
> > initialize the fault around order variable for pseries platform of
> > powerpc.

Sorry for not commenting earlier - just reminded by this ping to Ingo.

I didn't study your numbers, but nowhere did I see what PAGE_SIZE you use.

arch/powerpc/Kconfig suggests that Power supports base page size of
4k, 16k, 64k or 256k.

I would expect your optimal fault_around_order to depend very much on
the base page size.

Perhaps fault_around_size would provide a more useful default?

Hugh
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