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

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Message-ID: <CAGXu5j+d3fzKWNtmPF9tyMg7PzHsKWQZkhu5tFaThLTZue=3JQ@mail.gmail.com>
Date:	Sat, 3 Aug 2013 12:35:22 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Alex Thorlton <athorlton@....com>
Cc:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, 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>,
	Robin Holt <holt@....com>
Subject: Re: [PATCH] Add per-process flag to control thp

On Fri, Aug 2, 2013 at 1:34 PM, Alex Thorlton <athorlton@....com> wrote:
>> What kind of workloads are you talking about?
>
> Our benchmarking team has a list of several of the SPEC OMP benchmarks
> that perform significantly better when THP is disabled. I tried to get
> the list but one of our servers is acting up and I can't get to it
> right now :/
>
>> What's wrong with madvise? Could you elaborate?
>
> The main issue with using madvise is that it's not an option with static
> binaries, but there are also some users who have legacy Fortran code
> that they're not willing/able to change.
>
>> And I think thp_disabled should be reset to 0 on exec.
>
> The main purpose for this getting carried down from the parent process
> is that we'd like to be able to have a userland program set this flag on
> itself, and then spawn off children who will also carry the flag.
> This allows us to set the flag for programs where we're unable to modify
> the code, thus resolving the issues detailed above.

This could be done with LD_PRELOAD for uncontrolled binaries. Though
it does seem sensible to make it act like most personality flags do
(i.e. inherited).

-Kees

-- 
Kees Cook
Chrome OS Security
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