On Wed, May 25, 2016 at 08:48:17AM +0000, Li, Liang Z wrote: > > > > Suggestion to address all above comments: > > > > 1. allocate a bunch of pages and link them up, > > > > calculating the min and the max pfn. > > > > if max-min exceeds the allocated bitmap size, > > > > tell host. > > > > > > I am not sure if it works well in some cases, e.g. The allocated pages > > > are across a wide range and the max-min > limit is very frequently to be > > true. > > > Then, there will be many times of virtio transmission and it's bad for > > > performance improvement. Right? > > > > It's a tradeoff for sure. Measure it, see what the overhead is. > > > > Hi MST, > > I have measured the performance when using a 32K page bitmap, Just to make sure. Do you mean a 32Kbyte bitmap? Covering 1Gbyte of memory? > and inflate the balloon to 3GB > of an idle guest with 4GB RAM. Should take 3 requests then, right? > Now: > total inflating time: 338ms > the count of virtio data transmission: 373 Why was this so high? I would expect 3 transmissions. > the call count of madvise: 865 > > before: > total inflating time: 175ms > the count of virtio data transmission: 1 > the call count of madvise: 42 > > Maybe the result will be worse if the guest is not idle, or the guest has more RAM. > Do you want more data? > > Is it worth to do that? > > Liang Either my math is wrong or there's an implementation bug. > > > > > > > 2. limit allocated bitmap size to something reasonable. > > > > How about 32Kbytes? This is 256kilo bit in the map, which comes > > > > out to 1Giga bytes of memory in the balloon. > > > > > > So, even the VM has 1TB of RAM, the page bitmap will take 32MB of > > memory. > > > Maybe it's better to use a big page bitmap the save the pages > > > allocated by balloon, and split the big page bitmap to 32K bytes unit, then > > transfer one unit at a time. > > > > How is this different from what I said? > > > > > > > > Should we use a page bitmap to replace 'vb->pages' ? > > > > > > How about rolling back to use PFNs if the count of requested pages is a > > small number? > > > > > > Liang > > > > That's why we have start pfn. you can use that to pass even a single page > > without a lot of overhead. > > > > > > > -- > > > > > 1.9.1 > > > > -- > > > > 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 -- 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
