Thank you for reporting this. I'm currently evaluating this with some
benchmarking experiments and my current observation concurs with the
observations. I believe enabled=madvise is probably the best way
forward but I still have several more test scenarios to complete to
ensure we don't hit any unexpected performance regresions.
** Changed in: linux (Ubuntu)
Status: Incomplete => In Progress
** Changed in: linux (Ubuntu)
Importance: Undecided => High
** Changed in: linux (Ubuntu)
Assignee: (unassigned) => Colin Ian King (colin-king)
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https://bugs.launchpad.net/bugs/1703742
Title:
Transparent hugepages should default to enabled=madvise
Status in linux package in Ubuntu:
In Progress
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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