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Description of problem:
RHEL6 is missing this upstream performance optimization that avoids merging some VMAs which are cloned from the parent process:
commit 965f55dea0e331152fa53941a51e4e16f9f06fae
Author: Shaohua Li <shaohua.li>
Date: Tue May 24 17:11:20 2011 -0700
mmap: avoid merging cloned VMAs
Avoid merging a VMA with another VMA which is cloned from the parent process.
The cloned VMA shares the anon_vma lock with the parent process's VMA. If
we do the merge, more vmas (even the new range is only for current
process) use the perent process's anon_vma lock. This introduces
scalability issues. find_mergeable_anon_vma() already considers this
case.
Signed-off-by: Shaohua Li <shaohua.li>
Cc: Rik van Riel <riel>
Cc: Hugh Dickins <hughd>
Cc: Andi Kleen <andi>
Signed-off-by: Andrew Morton <akpm>
Signed-off-by: Linus Torvalds <torvalds>
Version-Release number of selected component (if applicable):
How reproducible:
Steps to Reproduce:
1.
2.
3.
Actual results:
Expected results:
Additional info:
Created attachment 515832[details]
reproducer (proof of concept)
On an unpatched kernel, at the end of output there is a single 6*pagesize VMA area for the child like this,
7fee32989000-7fee3298f000 -w-p 00000000 00:00 0
On a patched kernel, there are two 3*pagesize VMA areas like this,
7f55bbd47000-7f55bbd4a000 -w-p 00000000 00:00 0
7f55bbd4a000-7f55bbd4d000 -w-p 00000000 00:00 0
Tips for testing: also to make sure that micro-benchmark like perf to measure the performance improve for multiple page faults workloads like this. Here to get some inspiration - http://lwn.net/Articles/368105/
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.
http://rhn.redhat.com/errata/RHSA-2011-1530.html
Description of problem: RHEL6 is missing this upstream performance optimization that avoids merging some VMAs which are cloned from the parent process: commit 965f55dea0e331152fa53941a51e4e16f9f06fae Author: Shaohua Li <shaohua.li> Date: Tue May 24 17:11:20 2011 -0700 mmap: avoid merging cloned VMAs Avoid merging a VMA with another VMA which is cloned from the parent process. The cloned VMA shares the anon_vma lock with the parent process's VMA. If we do the merge, more vmas (even the new range is only for current process) use the perent process's anon_vma lock. This introduces scalability issues. find_mergeable_anon_vma() already considers this case. Signed-off-by: Shaohua Li <shaohua.li> Cc: Rik van Riel <riel> Cc: Hugh Dickins <hughd> Cc: Andi Kleen <andi> Signed-off-by: Andrew Morton <akpm> Signed-off-by: Linus Torvalds <torvalds> Version-Release number of selected component (if applicable): How reproducible: Steps to Reproduce: 1. 2. 3. Actual results: Expected results: Additional info: