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

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Date:	Tue, 19 Jan 2010 10:44:23 +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>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>, minchan.kim@...il.com
Subject: Re: [PATCH v6] add MAP_UNLOCKED mmap flag

Hi Gleb,

On Tue, Jan 19, 2010 at 10:26 AM, Gleb Natapov <gleb@...hat.com> wrote:
>> design would still be broken, no? Did you try using (or extending)
>> posix_madvise(MADV_DONTNEED) for the guest address space? It seems to
> After mlockall() I can't even allocate guest address space. Or do you mean
> instead of mlockall()? Then how MADV_DONTNEED will help? It just drops
> page table for the address range (which is not what I need) and does not
> have any long time effect.

Oh right, MADV_DONTNEED is no good.

On Tue, Jan 19, 2010 at 10:26 AM, Gleb Natapov <gleb@...hat.com> wrote:
>> 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.
>>
> I what to tell to VM "swap this, don't swap that" and as far as I see
> there is no other way to do it currently.

Yeah, which is why I was suggesting that maybe posix_madvise() needs
to be extended to have a MADV_NEED_BUT_LESS_IMPORTANT flag that can be
used as a hint by mm/vmscan.c to first swap the guest address spaces.

                        Pekka
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