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

[Jeff Dike <jdike@addtoit.com>]

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.

> 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.

> 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.

> 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.

				Jeff


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