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

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Message-ID: <20100119104058.GL14345@redhat.com>
Date:	Tue, 19 Jan 2010 12:40:58 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Pekka Enberg <penberg@...helsinki.fi>
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

On Tue, Jan 19, 2010 at 10:44:23AM +0200, Pekka Enberg wrote:
> 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.
> 
If such thing would exist may be I would have used it since swapping out
of a wrong page is not live or death matter in my case, but mlockall()
provides me with exactly what I need and without swapping out wrong
pages. Speaking about adding such madvise call wouldn't it be even
harder to justify? It obviously not good enough for real-time use and my
case, I admit, is unusual. Also if we start prioritise memory why stop
on binary, why not set value like "this memory is more important then
that memory by factor of 5"?

--
			Gleb.
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