Messages in this thread | | | Date | Thu, 25 Jul 2013 11:07:19 +0400 | From | Cyrill Gorcunov <> | Subject | Re: [PATCH] mm: Save soft-dirty bits on swapped pages |
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On Wed, Jul 24, 2013 at 12:40:22PM -0700, Andy Lutomirski wrote: > > Hmm. So there are at least three kinds of memory: > > Anonymous pages: soft-dirty works > Shared file-backed pages: soft-dirty does not work > Private file-backed pages: soft-dirty works (but see below) > > Perhaps another bit should be allocated to expose to userspace either > "soft-dirty", "soft-clean", or "soft-dirty unsupported"?
> There's another possible issue with private file-backed pages, though: > how do you distinguish clean-and-not-cowed from cowed-but-soft-clean? > (The former will reflect changes in the underlying file, I think, but > the latter won't.)
When fault happens with cow allocation (on write) the pte get soft dirty bit set (the code uses pte_mkdirty(entry) in __do_fault) and until we explicitly clean the bit it remains set. Or you mean something else?
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