linux-kernel - Re: [PATCH 2/6] ksm: dont allow overlap memory addresses registrations.

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Message-ID: <4A0181EA.3070600@redhat.com>
Date:	Wed, 06 May 2009 08:26:18 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Izik Eidus <ieidus@...hat.com>
CC:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	aarcange@...hat.com, chrisw@...hat.com, alan@...rguk.ukuu.org.uk,
	device@...ana.org, linux-mm@...ck.org, hugh@...itas.com,
	nickpiggin@...oo.com.au
Subject: Re: [PATCH 2/6] ksm: dont allow overlap memory addresses registrations.

Izik Eidus wrote:
> Rik van Riel wrote:
>> Izik Eidus wrote:
>>> subjects say it all.
>>
>> Not a very useful commit message.
>>
>> This makes me wonder, though.
>>
>> What happens if a user mmaps a 30MB memory region, registers it
>> with KSM and then unmaps the middle 10MB?
> 
> User cant break 30MB into smaller one.

The user can break up the underlying VMAs though.

I am just wondering out loud if we really want two
VMA-like objects in the kernel, the VMA itself and
a separate KSM object, with different semantics.

Maybe this is fine, but I do think it's a question
that needs to be thought about.

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