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Cause:
In a low-memory situation, a logic error causes glibc malloc to use mmap even if memory is available internally without requesting it from the kernel.
Consequence:
The malloc implementation in glibc could use excessively rely on mmap, resulting performance problems.
Fix:
The logic error is corrected and available memory is reused.
Result:
Application performance in low-memory situations should improve.
DescriptionSiddhesh Poyarekar
2015-08-21 16:00:41 UTC
Description of problem:
Due to the robust malloc changes, malloc functions may end up calling mmap prematurely if all arenas are contended but not corrupt. This is not a serious issue in the general case and its performance impact is also questionable because it is not clear if the contention is more expensive in terms of time than a system call. It is however expensive resource-wise if the block requests are significantly smaller than page size because that will create a lot of external holes.
See also: bug 1246713 for rhel-6, where this problem is one of two problems that the bug report mentioned.
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://rhn.redhat.com/errata/RHSA-2016-2573.html