linux-kernel - Re : vm: weird behaviour when munmapping

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Message-ID: <20061117134325.62026.qmail@web23114.mail.ird.yahoo.com>
Date:	Fri, 17 Nov 2006 13:43:25 +0000 (GMT)
From:	moreau francis <francis_moreau2000@...oo.fr>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re : vm: weird behaviour when munmapping

Peter Zijlstra wrote:
> On Fri, 2006-11-17 at 12:50 +0000, moreau francis wrote:
>>
>> lower vma: 0x2aaae000 -> 0x2aaaf000
>> upper vma: 0x2aaaf000 -> 0x2aab2000
> 
> that is the remaining VMA, not the new one; we trigger this code:
> 
>     /* Does it split the last one? */
>     last = find_vma(mm, end);
>     if (last && end > last->vm_start) {
>         int error = split_vma(mm, last, end, 1);
>         if (error)
>             return error;
>     }
> 
> So, since its the last VMA that needs to be split (there is only one),
> the new VMA is constructed before the old one. Like so:
> 
>   AAAAAAAAAAAAAAAAAAAAA
>   BBBBAAAAAAAAAAAAAAAAA
> 
> Then you proceed closing, in this case the new one: B.

Sorry but I don't understand why B is said to be the new one. OK
I can see why from the bit of code you pointed out but from a
logical point of view (ok maybe be me only) I'm unmapping 'BBBB'
segment, so 'BBBB' is going to be destroyed and therefore A is
the new one. Thereferore I would expect close(B), open(A)...

no ?

Francis

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