Re: subobj-rmap

[Martin J. Bligh]

>> 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.