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

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Message-ID: <84144f021001190007q54a334dfwed64189e6cf0b7c4@mail.gmail.com>
Date:	Tue, 19 Jan 2010 10:07:07 +0200
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Gleb Natapov <gleb@...hat.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, 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

Hi Gleb,

On Tue, Jan 19, 2010 at 9:52 AM, Gleb Natapov <gleb@...hat.com> wrote:
>> It would be probably useful if you could point us to the application
>> source code that actually wants this feature.
>>
> This is two line patch to qemu that calls mlockall(MCL_CURRENT|MCL_FUTURE)
> at the beginning of the main() and changes guest memory allocation to
> use MAP_UNLOCKED flag. All alternative solutions in this thread suggest
> that I should rewrite qemu + all library it uses. You see why I can't
> take them seriously?

Well, that's not going to be portable, is it, so the application
design would still be broken, no? Did you try using (or extending)
posix_madvise(MADV_DONTNEED) for the guest address space? It seems to
me that you're trying to use a big hammer (mlock) when a polite hint
for the VM would probably be sufficient for it do its job.

                        Pekka
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