[Devel] Re: [PATCH 16/28] [FLAT 1/6] Changes in data structures for flat model

[Pavel Emelianov]

sukadev at us.ibm.com wrote:
> Pavel Emelianov [xemul at openvz.org] wrote:
> | sukadev at us.ibm.com wrote:
> | > Pavel Emelianov [xemul at openvz.org] wrote:
> | > | This patch opens the flat model patches.
> | > | 
> | > | The flat model idea is that struct pid has two numbers. The first one 
> | > | (pid->nr) is a global one and is unique in the system. The second one 
> | > | (pid->vnr) is a virtual pid. It is used on the kernel user boundary only.
> | > 
> | > This approach duplicates 5 integers and 2 pointers per process for every
> | > process in the system. While this may not be expensive for processes that
> | > actually use multiple namespaces, doesn't it waste memory if majority of
> | > processes exist only in one namespace ?
> | 
> | task_struct alignment allows for it. so does the alignment of signal structure.
> | and please note that this comes with appropriate ifdefs around. the only problem
> | is with struct pid, but we're virtualizing it after all!
> 
> Hmm. I don't understand the last part "we are virtualizing 'struct pid'".
> Even so, with the FLAT model, every process will still have two
> pid_t values, two hash-chain links etc - no ?

I mean that since we're adding some extra functionality to the kernel
this is OK to extend the data structures. Moreover we have these changes
under appropriate ifdefs.

> | 
> | moreover - two integers and a pointer to the namespace is the minimal set of
> | fields for pid that is visible from two namespaces...
> 
> I ignored the pid_namespace pointer. But even a process that exists only
> in init_pid_ns would have the extra fields right ?

It will. But this is OK.

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