What were you trying to do that didn't work?

After moving to the vma maple tree in the 9.5 503 kernel, the median and mean completion time on certain syscalls, in particular mmap, mprotect, and munmap, take nearly twice as long. Certain optimization have improved this, but the median completion time even in the most recent upstream kernel version is still a large increase from the rbtree implementation.

What is the impact of this issue to you?

Latency sensitive workloads will incur performance issues when migrating.

Please provide the package NVR for which the bug is seen:

kernel-5.14.0-503.1.1.el9_5

How reproducible is this bug?:

always

Steps to reproduce

1. Boot to various kernels pre and post vma maple tree implementation kernel
2. run the reproducer
3. observe differences in results

Expected results

Red Hat Enterprise Linux 8 results

# ./mmap-test -z
Test: /dev/zero, MAP_PRIVATE
Ran 100000 iterations.
Average mmap() time:     0.421030 us
Average mprotect() time: 0.287795 us
Average munmap() time:   0.417753 us
Average total time:      1.126578 us

Actual results

Upstream

# ./mmap-test -z
Test: /dev/zero, MAP_PRIVATE
Ran 100000 iterations.
Average mmap() time:     1.060432 us
Average mprotect() time: 0.555376 us
Average munmap() time:   0.797092 us
Average total time:      2.412900 us

Red Hat Enterprise Linux 9

# ./mmap-test -z
Test: /dev/zero, MAP_PRIVATE
Ran 100000 iterations.
Average mmap() time:     1.120842 us
Average mprotect() time: 0.616725 us
Average munmap() time:   0.946954 us
Average total time:      2.684522 us