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Date: Mon, 5 Aug 2013 16:03:06 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Alex Thorlton <athorlton@sgi.com>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>, Mel Gorman <mgorman@suse.de>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Rik van Riel <riel@redhat.com>, Johannes Weiner <hannes@cmpxchg.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Sedat Dilek <sedat.dilek@gmail.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Dave Jones <davej@redhat.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        David Howells <dhowells@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Al Viro <viro@zeniv.linux.org.uk>, Oleg Nesterov <oleg@redhat.com>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
        Kees Cook <keescook@chromium.org>, Robin Holt <holt@sgi.com>
Subject: Re: [PATCHv2] Add per-process flag to control thp
Message-Id: <20130805160306.a620c88ba9098b98a0f93665@linux-foundation.org>
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On Fri, 2 Aug 2013 15:57:35 -0500 Alex Thorlton <athorlton@sgi.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.