Subject: Re: [Bug] mlockall() not working properly in 2.6.x
From: Zan Lynx <zlynx@acm.org>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Jan-Benedict Glaw <jbglaw@lug-owl.de>,
       Marc-Jano Knopp <pub_ml_lkml@marc-jano.de>,
       Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org
In-Reply-To: <1135014451.6051.23.camel@localhost.localdomain>
References: <20051218212123.GC4029@mjk.myfqdn.de>
	 <20051219022108.307e68b8.akpm@osdl.org>
	 <20051219114231.GA2830@mjk.myfqdn.de>  <20051219172735.GL13985@lug-owl.de>
	 <1135014451.6051.23.camel@localhost.localdomain>
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Date: Mon, 19 Dec 2005 11:38:35 -0700
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On Mon, 2005-12-19 at 17:47 +0000, Alan Cox wrote:
> On Llu, 2005-12-19 at 18:27 +0100, Jan-Benedict Glaw wrote:
> > > > that we did this because inheriting MCL_FUTURE is standards-incorre=
ct.
> > >=20
> > > Oh! So how can I make programs unswappable with kernel 2.6.x then?
> >=20
> > That would mean that you cannot just exec() another program that will
> > also be mlockall()ed. The new program has to do that on its own...
>=20
> mlockall MCL_FUTURE applies to this image only and the 2.6 behaviour is
> correct if less useful in some ways. It would be possible to add an
> inheriting MCL_ flag that was Linux specific but then how do you control
> the depth of inheritance ? If that isn't an issue it looks the easiest.
>=20
> Another possibility would be pmlockall(pid, flag), but that looks even
> more nasty if it races an exec.

How about clearing MCL_FUTURE on fork but allow exec to inherit it?
That way a parent process could fork, mlockall in the child and exec a
memlocked child.  A regular fork,exec by a memlocked parent would not
create a memlocked child.

Seems less messy than a new flag, while keeping the benefits.
--=20
Zan Lynx <zlynx@acm.org>

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