linux-kernel - Re: [PATCHv2] Add per-process flag to control thp

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Date:	Wed, 7 Aug 2013 20:49:41 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Alex Thorlton <athorlton@....com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Mel Gorman <mgorman@...e.de>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Sedat Dilek <sedat.dilek@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Dave Jones <davej@...hat.com>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	David Howells <dhowells@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Al Viro <viro@...iv.linux.org.uk>,
	Oleg Nesterov <oleg@...hat.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Kees Cook <keescook@...omium.org>, Robin Holt <holt@....com>
Subject: Re: [PATCHv2] Add per-process flag to control thp

On Tue, 6 Aug 2013, Alex Thorlton wrote:

> I've gotten my hands on some of the benchmarks/code that were used to
> originally uncover the performance issues we're seeing.  I'm currently
> trying to separate out the performance issues that are being caused by
> the kernel code from issues involving hardware - the cost of remote
> memory accesses is a bit higher on our systems with node controllers vs.
> glueless QPI/Hypertransport-based systems.  
> 

We've seen some issues where accessing remote hugepages causes performance 
degradations over accessing local pages that affects some workloads, but 
that seems like a mempolicy issue rather than madvise.  You probably want 
local hugepages but not fallback to remote hugepages before allocating 
local pages?  It would be interesting to see /proc/pid/numa_maps and 
/proc/pid/smaps for workloads that don't like thp.
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