Marcelo Tosatti <mtosatti@xxxxxxxxxx> wrote: > > If we do not mind scanning the bitmap twice, we can decouple the > > xchg loop and write protection, but it will be a bit slower, and in > > any case we need to hold mmu_lock until TLB is flushed. > > Why is it necessary to scan twice? Simply continuing to the next set > of pages, after dropping the lock, should be enough. We cannot drop the lock. Do you mean doing TLB flush each time before dropping the lock? > The potential problem i am referring to is: > > - kvm.git next + srcu-less series > average(ns) stdev ns/page pages improvement(%) > > 8497356.4 16441.0 32.4 256K -29 > > So 8ms for 1GB. Assuming it increases linearly, it would take > 400ms for get_dirty on a 50GB slot (most of that time spent > with mmu_lock held). Is this correct? Partly yes: my method mainly depends on the number of dirty pages, not slot size. But it is not a new problem: traversing all shadow pages for that also takes linearly increasing time. If that 1GB dirty memory is in a 50GB slot, my method will alleviate the latency really a lot compared to the current way. I do not want to imagine checking every shadow page in such a huge slot. Checking pages found in the dirty bitmap only should be better. Takuya -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
