On 07/24/2013 11:40 PM, Andy Lutomirski wrote: > On Wed, Jul 24, 2013 at 12:04 PM, Cyrill Gorcunov <gorcunov@xxxxxxxxx> wrote: >> On Wed, Jul 24, 2013 at 10:55:41PM +0400, Pavel Emelyanov wrote: >>>> >>>> Well, some part of information already lays in pte (such as 'file' bit, >>>> swap entries) so it looks natural i think to work on this level. but >>>> letme think if use page struct for that be more convenient... >>> >>> It hardly will be. Consider we have a page shared between two tasks, >>> then first one "touches" it and soft-dirty is put onto his PTE and, >>> subsequently, the page itself. The we go and clear sofr-dirty for the >>> 2nd task. What should we do with the soft-dirty bit on the page? >> >> Indeed, this won't help. Well then, bippidy-boppidy-boo, our >> pants are metaphorically on fire (c) > > 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) The shared file-backed pages case works, but unmap-map case doesn't preserve the soft-dirty bit. Just like the private file did. We'll fix this case next. > 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.) There's a bit called PAGE_FILE bit in /proc/pagemap file introduced with the 052fb0d635df5d49dfc85687d94e1a87bf09378d commit. Plz, refer to Documentation/vm/pagemap.txt and soft-dirty.txt, all this is described there pretty well. > --Andy Thanks, Pavel -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>