jm + madvise   1

Transparent huge pages implicated in Redis OOM
A nasty real-world prod error scenario worsened by THPs:
jemalloc(3) extensively uses madvise(2) to notify the operating system that it's done with a range of memory which it had previously malloc'ed. The page size on this machine is 2MB because transparent huge pages are in use. As such, a lot of the memory which is being marked with madvise(..., MADV_DONTNEED) is within substantially smaller ranges than 2MB. This means that the operating system never was able to evict pages which had ranges marked as MADV_DONTNEED because the entire page has to be unneeded to allow a page to be reused. Despite initially looking like a leak, the operating system itself was unable to free memory because of madvise(2) and transparent huge pages. This led to sustained memory pressure on the machine and redis-server eventually getting OOM killed.
oom-killer  oom  linux  ops  thp  jemalloc  huge-pages  madvise  redis  memory 
march 2015 by jm

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