Re: Swapping pagers out

[kod-e]

Marcus Brinkmann wrote:

> At Fri, 11 Feb 2005 15:38:40 +0100,
> "address@hidden" <address@hidden> wrote:
>  
>
> > Marcus Brinkmann <address@hidden> wrote:
> >
> >    
> >
> > > How does all of this answer your question?  Well, as soon as we have
> > > this, physmem could in fact be made to swap out the whole task (except
> > > for active DMA regions).  So, the constraints you mention that follow
> > > from the tex document in the source would not apply anymore.
> > >      
> > I don't think that any "default" pager should be able to swap out data
> > (because the task may have data it doesn't want to be paged out to the
> > swap, e.g. for security reasons, remember cached passwords).
> >    
AFAIR, "default" pager is provided by the PHYSMEM server,
which is of course trusted. _BUT_, if your task going to deal with
crucial data(i.e. passwords.. etc.), it'll have to use its own pager, which
knows which pages it can give out to PHYSMEM when it's asked for.
e.g. PHYSMEM ask for some pages from task, it refers to that tasks 
pager(right?),
and pager has its own policy on giving pages back to PHYSMEM
(well all pocily here is that it can hold Granted pages, and give out 
Extra ones).
And here, is where diference between Granted and Extra pages apear.
Task can hold it's Granted pages, and not give them to PHYSMEM on demand.
Which is not right for Extra pages. So if Extra pages contain some 
crucial data,
the tasks pager has some time(it must have, right?) to manipulate tasks 
pages
and all that crucial data mark(here i don't found any words to express 
it elseway),
remap, to Granted page.

And by the way, why we would want to swap out pagers? "To achieve more 
flexibility?"

If i'm not right here - sorry me.

> So, even if you have a lot of tasks, you should be able to
> give each a bit of resident memory, and completely swapping out a task
> is not a very important goal.  Am I wrong with this?
>  
I thought that the main diference between Granted and Extra pages is that
Granted pages are guaranteed to task, and can't be taken back py any pager.
So, task must have at least one G page to operate.

TFYA

 -- Kode