Re: [RFC] on general object IDs again

[Pavel Emelyanov <xemul@parallels.com>]

On 01/11/2012 10:19 PM, KOSAKI Motohiro wrote:
>> Hi Kosaki,
>>
>> the idea on user-space is something like
>>
>>  - collect all pids to dump
>>  - collect IDs for every pid
>>  - sort the IDs obtained
>>  - find the same IDs (which will be kind of find intersections in a sets of IDs) and
>>   set up CLONE_ flags on restore procedure as appropriate (for example if
>>   GEN_OBJ_ID_VM IDs for two or more tasks are the same we need to use CLONE_VM
>>   at restore time, and so on).
> 
> Then, you only need to compare. not any other calculation. i.e. only
> need id uniqueness.
> And any resource are referenced from tasks. so, can you reuse pid for
> this? example,
> two taska share one mm.
> 
> task-a(pid: 100)
>               |-----------------mm
> task-b(pid: 200)
> 
> 
> gen_obj_id(task-b, GEN_OBJ_ID_VM) return 100. (youngest pid of referenced tasks)

We can, but determining the youngest pid for an mm struct is O(N) algo.
Having N tasks with N mm_structs getting the sharing picture becomes O(N^2).

> .
>