4.15 is now available in Bionic.  Marking this Fix Released.

** Tags added: kernel

** Information type changed from Private to Public

** Also affects: linux (Ubuntu Bionic)
   Importance: Undecided
       Status: New

** Changed in: intel
       Status: New => Fix Released

** Changed in: linux (Ubuntu)
       Status: New => Fix Released

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  [Feature] [HMEM] VMA based swap readahead

Status in intel:
  Fix Released
Status in linux package in Ubuntu:
  Fix Released
Status in linux source package in Bionic:
  Fix Released

Bug description:

  The swap readahead is a important mechanism to reduce the swap in
  latency. But the original swap readahead algorithm has some issues.

  a) The original swap readahead algorithm does readahead based on the
  consecutive blocks in swap device. But the consecutive blocks in
  swap device just reflect the order of page reclaiming, but don't
  necessarily reflect the access sequence in RAM. Although for some
  workloads (such as whole system pure sequential workload), it
  works, but in general, it doesn't work well for more complex access
  pattern, such as combined workloads (sequential and random workload
  runs together) or changing accessing patterns in workload.

  b) The original swap readahead algorithm just turns random read into
  sequential read, but doesn’t parallel CPU and disk operations.
  This can reduce the average latency and the lowest latency, but
  doesn’t help much for high percentile latency (like 90%, 95%,

  To solve the above issues, A VMA based swap readahead algorithm is designed.
  When the page fault occurs, the pages along the access direction will
  be checked and the swapped out pages will be readahead if they fall
  inside the readahead window. There is one readahead window state for
  each VMA, to reflect the different access patterns for different VMAs.
  The readahead window is scaled based on whether the accessed page is
  consecutive in virtual address with the previous accessed page. If
  so, the readahead window will be extended, otherwise, the readahead
  window will be shrunk rapidly.

  Target Kernel: 4.14
  Target Release: 18.04

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