Comment 8 for bug 1461620

I'm running the NUMA tests on 3.13 for some time now and it looks like the change did not introduce any regression...

$ uname -a
Linux sf00079894trusty 3.13.11-ckt22-201507231149 #2 SMP Thu Jul 23 13:45:04 BRT 2015 x86_64 x86_64 x86_64 GNU/Linux

I'm using a virtualized 16 Domains / 16 CPUs NUMA environment with the stress test tool:

$ sudo numactl -H
available: 16 nodes (0-15)
node 0 cpus: 0
node 0 size: 363 MB
node 0 free: 23 MB
node 1 cpus: 1
node 1 size: 121 MB
node 1 free: 7 MB
node 2 cpus: 2
node 2 size: 377 MB
node 2 free: 23 MB
node 3 cpus: 3
node 3 size: 377 MB
node 3 free: 23 MB
node 4 cpus: 4
node 4 size: 377 MB
node 4 free: 23 MB
node 5 cpus: 5
node 5 size: 377 MB
node 5 free: 23 MB
node 6 cpus: 6
node 6 size: 377 MB
node 6 free: 35 MB
node 7 cpus: 7
node 7 size: 313 MB
node 7 free: 19 MB
node 8 cpus: 8
node 8 size: 377 MB
node 8 free: 61 MB
node 9 cpus: 9
node 9 size: 377 MB
node 9 free: 57 MB
node 10 cpus: 10
node 10 size: 377 MB
node 10 free: 63 MB
node 11 cpus: 11
node 11 size: 377 MB
node 11 free: 30 MB
node 12 cpus: 12
node 12 size: 377 MB
node 12 free: 67 MB
node 13 cpus: 13
node 13 size: 377 MB
node 13 free: 68 MB
node 14 cpus: 14
node 14 size: 377 MB
node 14 free: 68 MB
node 15 cpus: 15
node 15 size: 377 MB
node 15 free: 64 MB

$ sudo stress --vm 16 --vm-bytes 314572800 --vm-stride 1 --vm-keep &

Causing memory allocations of around 300MB on each node and "touching" every byte of the allocation (causing all the pages to be "hot" on the CPU running).

And generating concurrency:

$ sudo stress --cpu 16 &

So kernel scheduler has to migrate tasks, triggering the buggy logic's fix. I can confirm the logic is being triggered by using ftrace:

$ sudo trace-cmd record -p function -l numa_migrate_preferred -l task_numa_migrate -l migrate_swap -l stop_two_cpus
$ sudo trace-cmd report | grep stop_two_cpus | wc -l162

And can't find any regression.

I'll let the tests to run a bit more and will suggest the fix to our kernel team to merge it as a Stable Release Update for Trusty, Utopic and Vivid.