Re: [RFC 2.6.11-rc2-mm2 0/7] mm: manual page migration -- overview II

[Andi Kleen]

On Tue, Feb 22, 2005 at 12:45:21PM -0600, Ray Bryant wrote:
> Andi Kleen wrote:
> 
> >
> >How about you add the va_start, va_end but only accept them 
> >when pid is 0 (= current process). Otherwise enforce with EINVAL
> >that they are both 0. This way you could map the
> >shared object into the batch manager, migrate it there, then
> >mark it somehow to not be migrated further, and then
> >migrate the anonymous pages using migrate_pages(pid, ...) 
> >
> 
> We'd have to use up a struct page flag (PG_MIGRATED?) to mark
> the page as migrated to keep the call to migrate_pages() for
> the anonymous pages from migrating the pages again.  Then we'd

I was more thinking of a new mempolicy or a flag for one.
Flag would be probably better.  No need to keep state in struct page.

> How about ignoring the va_start and va_end values unless
> either:
> 
>       pid == current->pid
>   or  current->euid == 0 /* we're root */
> 
> I like the first check a bit better than checking for 0.  Are
> there other system calls that follow that convention (e. g.
> pid = 0 implies current?)
> 
> The second check lets a sufficiently responsible task manipulate
> other tasks.  This task can choose to have the target tasks
> suspended before it starts fussing with them.

I don't like that. The idea behind this restriction is to simplify
things by making sure only processes change their own VM. Letting
root overwrite this doesn't make much sense.

-Andi
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