Re: Extensions to mincore

["Stephen C. Tweedie" <sct@scot.redhat.com>]

On Tue, Mar 21, 2000 at 04:15:07PM +0100, Jamie Lokier wrote:
> > Dirty GC wise the page has changes since the last GC pass over it.
> 
> Of course, I thought that was obvious :-)
> 
> You're right, that for GC the "!dirty" bit has to mean "since the last
> time we called mincore".

And that information is not maintained anywhere.  In fact, it basically
_can't_ be maintained, since the hardware only maintains one bit and
we already use that dirty bit.  The only way round this is to use
mprotect-style munging.

> All threads sharing a page have to synchronise their mincore calls for
> that page, but that situation is no different to the SEGV method: all
> threads have to synchronise with the information collected from that,
> too.

It's not about synchronising between mincore calls, it's about 
synchronising mincore calls on one CPU with direct memory references
modifying page tables on another CPU.

--Stephen
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