Linux Page Faults, MMAP, and userfaultfd for faster VM boots
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Re: Linux Page Faults, MMAP, and userfaultfd for faster VM boots
#2Oh neat, a post I actually know something about! I worked a lot on userfaultfd performance for GCE's live migration post-copy a couple years ago. Or more specifically, I worked on mechanisms to avoid it entirely- due to lock contention in the kennel, faults become veeeerry slow as the number of vcpus scales, and as it happens VMs these days can have a lot of vcpus
Re: Linux Page Faults, MMAP, and userfaultfd for faster VM boots
#3> Userfaultfd is a Linux mechanism, available since kernel 4.3, with additional event features like non-cooperative mode and fork/remap/remove tracking added in 4.11, that lets a userspace thread intercept and handle page faults.
Is this the same feature Windows has had forever, or is there more to it?
Re: Linux Page Faults, MMAP, and userfaultfd for faster VM boots
#4Oh neat, a post I actually know something about! I worked a lot on userfaultfd performance for GCE's live migration post-copy a couple years ago. Or more specifically, I worked on mechanisms to avoid it entirely- due to lock contention in the kennel, faults become veeeerry slow as the number of vcpus scales, and as it happens VMs these days can have a lot of vcpus
that's very interesting! I was noticing page vault storm on live migrations as well and I wonder if that's what you were running into / mentioning here regarding the lock contention
Re: Linux Page Faults, MMAP, and userfaultfd for faster VM boots
#5Oh neat, a post I actually know something about! I worked a lot on userfaultfd performance for GCE's live migration post-copy a couple years ago. Or more specifically, I worked on mechanisms to avoid it entirely- due to lock contention in the kennel, faults become veeeerry slow as the number of vcpus scales, and as it happens VMs these days can have a lot of vcpus
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