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

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Date:	Mon, 5 Aug 2013 16:03:06 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Alex Thorlton <athorlton@....com>
Cc:	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 Fri, 2 Aug 2013 15:57:35 -0500 Alex Thorlton <athorlton@....com> wrote:

> This patch implements functionality to allow processes to disable the use of
> transparent hugepages through the prctl syscall.
> 
> We've determined that some jobs perform significantly better with thp disabled,
> and we needed a way to control thp on a per-process basis, without relying on
> madvise.

What everyone else said, plus...

I worry about the inherit-across-fork thing.  A scenario we should
think about is where the user doesn't build his own executables.  So he
writes a little wrapper which runs prctl(PR_SET_THP_DISABLED, 0) then
execs the third-party-app.  But what happens if that app execs children
who *do* want THP?  He has to hunt down and wrap those as well?

It all seems a bit unwieldy.  I wonder if controlling it via the ELF
header would be more practical.


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