Re: [patch 4/6] mm: merge populate and nopage into fault (fixes nonlinear)

[Nick Piggin]

On Wed, Mar 07, 2007 at 01:07:56AM -0800, Andrew Morton wrote:
> On Wed, 07 Mar 2007 09:51:57 +0100 Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
> 
> > > > Dirty page accounting doesn't work either on
> > > > non-linear mappings
> > > 
> > > It doesn't?  Confused - these things don't have anything to do with each
> > > other do they?
> > 
> > Look in page_mkclean().  Where does it handle non-linear mappings?
> > 
> 
> OK, I'd forgotten about that.  It won't break dirty memory accounting,
> but it'll potentially break dirty memory balancing.
> 
> If we have the wrong page (due to nonlinear), page_check_address() will
> fail and we'll leave the pte dirty.  That puts us back to the pre-2.6.17
> algorithms and I guess it'll break the msync guarantees.
> 
> Peter, I thought we went through the nonlinear problem ages ago and decided
> it was OK?

msync breakage is bad, but otherwise I don't know that we care about
dirty page writeout efficiency.

But I think we discovered that those msync changes are bogus anyway
becuase there is a small race window where pte could be dirtied without
page being set dirty?


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