Bug 1255822

Summary: glibc: malloc may fall back to calling mmap prematurely if arenas are contended
Product: Red Hat Enterprise Linux 7 Reporter: Siddhesh Poyarekar <spoyarek>
Component: glibcAssignee: Carlos O'Donell <codonell>
Status: CLOSED ERRATA QA Contact: Arjun Shankar <ashankar>
Severity: unspecified Docs Contact:
Priority: unspecified    
Version: 7.3CC: ashankar, fweimer, mcermak, mkolar, mnewsome, pfrankli
Target Milestone: rcKeywords: Patch
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
See Also: https://bugzilla.redhat.com/show_bug.cgi?id=1246713
Fixed In Version: Doc Type: Bug Fix
Doc Text:
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.
Story Points: ---
Clone Of:
: 1348620 (view as bug list) Environment:
Last Closed: 2016-11-03 04:25:03 EDT Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---
Bug Depends On: 1348620    
Bug Blocks: 1297579, 1313485    
Description Flags
glibc-rh1245731-4.patch none

Description Siddhesh Poyarekar 2015-08-21 12:00:41 EDT
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.
Comment 6 Florian Weimer 2016-06-21 11:10 EDT
Created attachment 1170318 [details]

This is the patch which went into rhel-6.7.z.
Comment 7 Florian Weimer 2016-06-21 11:22:21 EDT
Proposed upstream fix: https://sourceware.org/ml/libc-alpha/2016-06/msg00815.html
Comment 14 errata-xmlrpc 2016-11-03 04:25:03 EDT
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.