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

From: Cyrill Gorcunov
Date: Wed Jul 24 2013 - 12:37:41 EST

On Wed, Jul 24, 2013 at 09:23:14AM -0700, Andy Lutomirski wrote:
> On Wed, Jul 24, 2013 at 9:08 AM, Cyrill Gorcunov <gorcunov@xxxxxxxxx> wrote:
> > Andy Lutomirski reported that in case if a page with _PAGE_SOFT_DIRTY
> > bit set get swapped out, the bit is getting lost and no longer
> > available when pte read back.
> Potentially silly question (due to my completely lack of understanding
> of how swapping works in Linux): what about file-backed pages?
> (Arguably these would be best supported by filesystems instead of by
> the core vm, in which case it might make sense to drop soft-dirty
> support for these pages entirely.)

Hi Andy, if I understand you correctly "file-backed pages" are carried
in pte with _PAGE_FILE bit set and the swap soft-dirty bit won't be
used on them but _PAGE_SOFT_DIRTY will be set on write if only I've
not missed something obvious (Pavel?).
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