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[Stefan Bader <stefan.bader@xxxxxxxxxxxxx>]

** Changed in: linux (Ubuntu Zesty)
       Status: In Progress => Won't Fix

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https://bugs.launchpad.net/bugs/1703742

Title:
  Transparent hugepages should default to enabled=madvise

Status in linux package in Ubuntu:
  Fix Released
Status in linux-gke package in Ubuntu:
  Fix Committed
Status in linux source package in Xenial:
  In Progress
Status in linux-gke source package in Xenial:
  Fix Released
Status in linux source package in Yakkety:
  Won't Fix
Status in linux source package in Zesty:
  Won't Fix
Status in linux source package in Artful:
  Fix Released

Bug description:
  SRU Justification, Zesty, Xenial

  [Impact]

  Ubuntu kernels should default transparent_hugepages to
  enabled=madvise, not enabled=always

  (this corresponds to TRANSPARENT_HUGEPAGE_MADVISE=y in .config).

  I've blogged about this at some length here:
  https://blog.nelhage.com/post/transparent-hugepages/ but here is a
  summary:

  Transparent Hugepages are a feature that allows the kernel to attempt
  to automatically back any anonymous maps with "huge" 2MiB page tables,
  instead of the normal 4k entries. It can produce small net performance
  gains in certain benchmarks, but also has numerous downsides, in the
  form of apparent memory leaks and 30% slowdowns or worse for some
  applications. Many popular pieces of software now refuse to run with
  hugepages enabled because of known performance issues.

  Examples of problem reports:
  MongoDB: https://docs.mongodb.com/manual/tutorial/transparent-huge-pages/
  Oracle: https://blogs.oracle.com/linux/entry/performance_issues_with_transparent_huge
  Splunk: https://docs.splunk.com/Documentation/Splunk/6.5.2/ReleaseNotes/SplunkandTHP
  Go runtime: https://github.com/golang/go/issues/8832
  jemalloc: https://blog.digitalocean.com/transparent-huge-pages-and-alternative-memory-allocators/
  node.js: https://github.com/nodejs/node/issues/11077

  Setting `enabled=madvise` enables applications that know they benefit
  from transparent huge pages to opt-in to this feature, while
  eliminating all the problematic behavior for other applications. Note
  also that transparent hugepage settings don't affect the use of
  explicit hugepages via hugetlbfs or mmap(…, MAP_HUGETLB, …)

  [Fix]
  Enable CONFIG_TRANSPARENT_HUGEPAGE_MADVISE=y

  [Regression Potential]
  May marginally impact performance, but the benefits of madvise'd huge transparent hugepage over-weigh this considerably.

  This has been enabled in Artful since July (and in Bionic) and we've
  not seen any regression reports, so we are confident this has minimal
  impact.

  [Testcase]
  Kernel ADT tests and stress-ng memory tests should not show any regressions.

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