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

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

Title:
  Transparent hugepages should default to enabled=madvise

Status in linux package in Ubuntu:
  Incomplete

Bug description:
  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, …)

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