On 7/25/19 4:00 PM, Alexander Duyck wrote: > On Thu, 2019-07-25 at 14:25 -0400, Nitesh Narayan Lal wrote: >> On 7/25/19 12:16 PM, Alexander Duyck wrote: >>> On Thu, 2019-07-25 at 11:16 -0400, Michael S. Tsirkin wrote: >>>> On Thu, Jul 25, 2019 at 08:05:30AM -0700, Alexander Duyck wrote: >>>>> On Thu, 2019-07-25 at 07:35 -0400, Nitesh Narayan Lal wrote: >>>>>> On 7/24/19 6:03 PM, Alexander Duyck wrote: >>>>>>> On Wed, 2019-07-24 at 17:38 -0400, Michael S. Tsirkin wrote: >>>>>>>> On Wed, Jul 24, 2019 at 10:12:10AM -0700, Alexander Duyck wrote: >>>>>>>>> From: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx> >>>>>>>>> > <snip> > > >>> Ideally we should be able >>> to provide the hints and have them feed whatever is supposed to be using >>> them. So for example I could probably look at also clearing the bitmaps >>> when migration is in process. >>> >>> Also, I am wonder if the free page hints would be redundant with the form >>> of page hinting/reporting that I have since we should be migrating a much >>> smaller footprint anyway if the pages have been madvised away before we >>> even start the migration. >>> >>>> FWIW Nitesh's RFC does not have this limitation. >>> Yes, but there are also limitations to his approach. For example the fact >>> that the bitmap it maintains is back to being a hint rather then being >>> very exact. >> True. >> >> >>> As a result you could end up walking the bitmap for a while >>> clearing bits without ever finding a free page. >> Are referring to the overhead which will be introduced due to bitmap scanning on >> very large guests? > Yes. One concern I have had is that for large memory footprints the RFC > would end up having a large number of false positives on an highly active > system. I am worried it will result in a feedback loop where having more > false hits slows down your processing speed, and the slower your > processing speed the more likely you are to encounter more false hits. > > It is definitely an interesting thing to see, I intend to test such a scenario with large guest before my next posting. -- Thanks Nitesh
