On Wed, Jul 24, 2013 at 9:37 AM, Cyrill Gorcunov <gorcunov@xxxxxxxxx> wrote: > 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?). If I understand this stuff correctly, the vmscan code calls try_to_unmap when it reclaims memory, which makes its way into try_to_unmap_one, which clears the pte (and loses the soft-dirty bit). --Andy -- 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>