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Date: Sun, 06 Apr 2003 15:03:03 -0700
From: "Martin J. Bligh" <mbligh@aracnet.com>
To: Rik van Riel <riel@surriel.com>
cc: Alan Cox <alan@lxorguk.ukuu.org.uk>, Andrew Morton <akpm@digeo.com>,
       andrea@suse.de, mingo@elte.hu, hugh@veritas.com, dmccr@us.ibm.com,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       linux-mm@kvack.org, Bill Irwin <wli@holomorphy.com>
Subject: Re: subobj-rmap
Message-ID: <1600000.1049666582@[10.10.2.4]>
In-Reply-To: <Pine.LNX.4.44.0304061737510.2296-100000@chimarrao.boston.redhat.com>
References: <Pine.LNX.4.44.0304061737510.2296-100000@chimarrao.boston.redhat.com>
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>> Supposing we keep a list of areas (hung from the address_space) that 
>> describes independant linear ranges of memory that have the same set
>> of vma's mapping them (call those subobjects). Each subobject has a
>> chain of vma's from it that are mapping that subobject.
>> 
>> address_space ---> subobject ---> subobject ---> subobject ---> subobject
>>                        |              |              |              | 
>>                        v              v              v              v
>>                       vma            vma            vma            vma
>>                        |                             |              | 
>>                        v                             v              v
>>                       vma                           vma            vma
>>                        |                             |        
>>                        v                             v        
>>                       vma                           vma       
> 
> OK, lets say we have a file of 1000 pages, or
> offsets 0 to 999, with the following mappings:
> 
> VMA A:   0-999
> VMA B:   0-200
> VMA C: 150-400
> VMA D: 300-500
> VMA E: 300-500
> VMA F:   0-999
> 
> How would you describe these with independant regions ?

Good question to illustrate with.
Extra spacing added just for ease of reading:

0-150 -> 150-200 -> 200-300 -> 300-400 -> 400-500 -> 500-999
 A          A          A          A          A          A
 B          B
            C          C          C 
                                  D          D          
                                  E          E          
 F          F          F          F          F          F

> For VMAs D & E and A & F it's a no-brainer,
> but for Oracle shared memory you shouldn't
> assume that you have any similar mappings

We can always leave the sys_remap_file_pages stuff using pte_chains,
and should certainly do that at first. But doing it for normal stuff
should be less controversial, I think.

M.