Re: [uml-devel] a question about sigsetjmp() in copy_from/to_user()

[Blaisorblade <blaisorblade@yahoo.it>]

On Sunday 02 October 2005 03:03, Jeff Dike wrote:
> On Thu, Sep 29, 2005 at 02:09:27PM +0200, Blaisorblade wrote:
> > Again, that page is not bad. There is no page yet for this address, and
> > the host won't allocate one for now.

> It is bad in the sense that, unless some space is freed on that mount, a
> reference to the page will always fault.
Sorry, any reference will fault, unless it is done on a allocated present 
page, which the UML kernel freed but the host didn't. And remember, btw, 
you've planned to make this impossible...
> > Ok, this makes a bit of sense, even if IMHO it doesn't work, I now see
> > your point (but I still insist with what said above).

> Explain why it doesn't work.
Below.
> > However, even a dirtied page could be "bad", if it has been swapped. If
> > we're getting a SIGBUS, it meant that it didn't succeed in freeing any
> > memory.

> No it can't.  A swapped page still counts as occupying space in the
> filesystem. If a page was successfully allocated, then accesses to it will
> always succeed, even if it needs to be swapped in.

Sorry, Jeff, which page are you going to evict? It can be a dirty page. Unless 
you mean that since that page is still accounted in the FS, Linux will leave 
a RAM page free to allow it to be re-read, while still swapping the page.

You didn't obviously mean this absurdity (why swap it in first place), but I 
don't catch what's missing to you.

> > And, frankly, unless the UML ram file is kept on ramfs (which is
> > RAM-only), it can be swapped (both for disk-based filesystem and for
> > tmpfs). So, I don't think what you suggest could work.

> Swapping makes no difference.
Realoding pages means freeing RAM to leave place to them.
-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade

		
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