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

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Date:	Wed, 7 Oct 2009 22:47:18 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Olivier Galibert <galibert@...ox.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linux-api@...r.kernel.org
Subject: Re: [PATCH][RFC] add MAP_UNLOCKED mmap flag

On Wed, Oct 07, 2009 at 10:10:17PM +0200, Olivier Galibert wrote:
> On Wed, Oct 07, 2009 at 08:59:52PM +0200, Gleb Natapov wrote:
> > On Wed, Oct 07, 2009 at 08:50:54PM +0200, Olivier Galibert wrote:
> > > On Tue, Oct 06, 2009 at 02:16:03PM +0200, Gleb Natapov wrote:
> > > > I did. It allows me to achieve something I can't now. Steps you provide
> > > > just don't fit my needs. I need all memory areas (current and feature) to be
> > > > locked except one. Very big one. You propose to lock memory at some
> > > > arbitrary point and from that point on all newly mapped memory areas will
> > > > be unlocked. Don't you see it is different?
> > > 
> > > What about mlockall(MCL_CURRENT); mmap(...); mlockall(MCL_FUTURE);?
> > > Or toggle MCL_FUTURE if a mlockall call can stop it?
> > > 
> > This may work. And MCL_FUTURE can be toggled, but this is not thread
> > safe.
> 
> Just ensure that your one special mmap is done with the other threads
> not currently allocating stuff.  It's probably a synchronization point
> for the whole process anyway.
> 
How can you stop other threads and libraries from calling malloc()? And if
it is two special allocations? Or many mmap(big file)/munmap(big file)?
This is the same issue as opening file CLOEXEC atomically. Why not
prevent other thread from calling fork() instead of adding flags to
bunch of system calls.

--
			Gleb.
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