linux-kernel - Re: [PATCH v6] add MAP

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Date:	Mon, 18 Jan 2010 17:01:59 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Pekka Enberg <penberg@...helsinki.fi>, linux-mm@...ck.org,
	kosaki.motohiro@...fujitsu.com, linux-kernel@...r.kernel.org,
	linux-api@...r.kernel.org, akpm@...ux-foundation.org,
	andrew.c.morrow@...il.com,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v6] add MAP_UNLOCKED mmap flag

On Mon, Jan 18, 2010 at 03:49:58PM +0100, Peter Zijlstra wrote:
> On Mon, 2010-01-18 at 14:32 +0000, Alan Cox wrote:
> > > this kind of control. As of use of mlockall(MCL_FUTURE) how can I make
> > > sure that all memory allocated behind my application's back (by dynamic
> > > linker, libraries, stack) will be locked otherwise?
> > 
> > If you add this flag you can't do that anyway - some library will
> > helpfully start up using it and then you are completely stuffed or will
> > be back in two or three years adding MLOCKALL_ALWAYS.
> 
> Agreed, mlockall() is a very bad interface and should not be used for a
> plethora of reasons, this being one of them.
> 
There are valid uses for mlockall() and even if the interface is bad there
is no alternative right now, so why not fix one of it problems?

> The thing is, if you cant trust your library to do sane things, then
> don't use it.
> 
Agreed, the are things that sane library should never do: exit() or output
debug info to stdio or meddle with memory mlock/munlock behind application's
back.

--
			Gleb.
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