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

From: Andy Lutomirski
Date: Fri Jul 26 2013 - 16:55:37 EST

On Fri, Jul 26, 2013 at 1:18 PM, Cyrill Gorcunov <gorcunov@xxxxxxxxx> wrote:
> Andy reported that if file page get reclaimed we loose soft-dirty bit
> if it was there, so save _PAGE_BIT_SOFT_DIRTY bit when page address
> get encoded into pte entry. Thus when #pf happens on such non-present
> pte we can restore it back.

Unless I'm misunderstanding this, it's saving the bit in the
non-present PTE. This sounds wrong -- what happens if the entire pmd
(or whatever the next level is called) gets zapped? (Also, what
happens if you unmap a file and map a different file there?)

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