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

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Message-ID: <20130804141928.GA17935@redhat.com>
Date:	Sun, 4 Aug 2013 16:19:28 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Kees Cook <keescook@...omium.org>
Cc:	Alex Thorlton <athorlton@....com>,
	"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>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Robin Holt <holt@....com>
Subject: Re: [PATCH] Add per-process flag to control thp

On 08/03, Kees Cook wrote:
>
> On Fri, Aug 2, 2013 at 1:34 PM, Alex Thorlton <athorlton@....com> wrote:
> >
> >> 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).

It is only inheritable if the process is single-threaded.

And even if it is single-threaded I can't understand how it can really
help.

OK, transparent_hugepage_enabled() checks ->thp_disabled, but this is
the fault path. But this flag can't hide the task from khugepaged and
collapse_huge_page ?

I still think this should be mm flag. And we have MMF_INIT_MASK, it
can be inheritable.

Oleg.

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