Re: Extensions to mincore

[lars brinkhoff <lars.brinkhoff@intermec.com>]

"Eric W. Biederman" wrote:
> Jamie Lokier <jamie.lokier@cern.ch> writes:
> > > > [Aside: is there the possibility to have mincore return the "!accessed"
> > > > and "!dirty" bits of each page, perhaps as bits 1 and 2 of the returned
> > > > bytes?  I can imagine a bunch of garbage collection algorithms that
> > > > could make good use of those bits.  Currently some GC systems mprotect()
> > > > regions and unprotect them on SEGV -- simply reading the !dirty status
> > > > would obviously be much simpler and faster.]
> 
> Dirty kernel wise means the page needs to be swapped out. Clean kernel
> wise mean the page is in the swap cache, and hasn't been written
> since it was swapped in.
> 
> Dirty GC wise the page has changes since the last GC pass over it.
> 
> It is very easy to conceive of a case where a dirty GC'd page swapped
> out, and then swapped in before someone got to looking at it.  So
> kernel Clean/Dirty has no connection with GC Clean/Dirty.
> 
> Please, please don't mess with this for a 2.4 timeframe.

For user-space paging, it would be great to know the kernel sense of the
clean/dirty
status of pages.  Perhaps something to be considered for 2.5.
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