On Wed, Aug 21, 2013 at 05:56:08PM +0100, David Vrabel wrote: > > > > And I asked David to point me how it happens, because I don't > > understand at which point pse bit get analized when page is > > not present. > > As Jan said, we're concerned that the bit was being used on present PTEs > and not just non-present ones. From a more careful look at this code > this does not appear to be the case. > > However, I do find the use of PTE bits in this way somewhat fragile. > What other potential corner cases might still remain that will require > further games with PTE bits?
OK, so this is not a bug finally. The problem is that 2 level pte is quite small and 7th bit is the only one spare I can use for soft dirty tracking when page get swapped out. And swap engine is very depending on pte being non-present, so we are on a safe side. > FWIW, Xen uses a separate dirty log to track which pages have become > dirty since the log was last cleared. Such a dirty log seems more > efficient than having scan all the PTEs looking for the soft dirty bits > and then having to scan them all again to clear them (particularly if > you need multiple passes because the task is still running and > continuing to dirty pages). -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/