Re: [PATCH] mm: Save soft-dirty bits on file pages

From: Cyrill Gorcunov
Date: Sat Jul 27 2013 - 02:25:21 EST

On Fri, Jul 26, 2013 at 02:36:51PM -0700, Andy Lutomirski wrote:
> >> Unless I'm misunderstanding this, it's saving the bit in the
> >> non-present PTE. This sounds wrong -- what happens if the entire pmd
> >
> > It's the same as encoding pgoff in pte entry (pte is not present),
> > but together with pgoff we save soft-bit status, later on #pf we decode
> > pgoff and restore softbit back if it was there, pte itself can't disappear
> > since it holds pgoff information.
> Isn't that only the case for nonlinear mappings?

Andy, I'm somehow lost, pte either exist with file encoded, either not,
when pud/ptes are zapped and any access to it should cause #pf pointing
kernel to read/write data from file to a page, if it happens on write
the pte is obtaining dirty bit (which always set together with soft
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