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

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Message-ID: <20091006102136.GH9832@redhat.com>
Date:	Tue, 6 Oct 2009 12:21:36 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linux-api@...r.kernel.org
Subject: Re: [PATCH][RFC] add MAP_UNLOCKED mmap flag

On Tue, Oct 06, 2009 at 07:11:06PM +0900, KOSAKI Motohiro wrote:
> Hi
> 
> > If application does mlockall(MCL_FUTURE) it is no longer possible to
> > mmap file bigger than main memory or allocate big area of anonymous
> > memory. Sometimes it is desirable to lock everything related to program
> > execution into memory, but still be able to mmap big file or allocate
> > huge amount of memory and allow OS to swap them on demand. MAP_UNLOCKED
> > allows to do that.
> > 
> > Signed-off-by: Gleb Natapov <gleb@...hat.com>
> 
> Why don't you use explicit munlock()?
Because mmap will fail before I'll have a chance to run munlock on it.
Actually when I run my process inside memory limited container host dies
(I suppose trashing, but haven't checked).

> Plus, Can you please elabrate which workload nedd this feature?
> 
I wanted to run kvm with qemu process locked in memory, but guest memory
unlocked. And guest memory is bigger then host memory in the case I am
testing. I found out that it is impossible currently.

--
			Gleb.
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