I would also not touch the numa balancing logic at this stage and
rather
see how the current implementation behaves.
I agree we would prefer start from something simpler and see how it
works.
The "twice access" optimization is aimed to reduce the PMEM
bandwidth burden
since the bandwidth of PMEM is scarce resource. I did compare "twice
access"
to "no twice access", it does save a lot bandwidth for some once-off
access
pattern. For example, when running stress test with mmtest's
usemem-stress-numa-compact. The kernel would promote ~600,000 pages
with
"twice access" in 4 hours, but it would promote ~80,000,000 pages
without
"twice access".
I pressume this is a result of a synthetic workload, right? Or do you
have any numbers for a real life usecase?
The test just uses usemem.
I tried to run some more real life like usecases, the below shows the
result by running mmtest's db-sysbench-mariadb-oltp-rw-medium test,
which is a typical database workload, with and w/o "twice access"
optimization.
w/ w/o
promotion 32771 312250
We can see the kernel did 10x promotion w/o "twice access" optimization.
I also tried kernel-devel and redis tests in mmtest, but they can't
generate enough memory pressure, so I had to run usemem test to generate
memory pressure. However, this brought in huge noise, particularly for
the w/o "twice access" case. But, the mysql test should be able to
demonstrate the improvement achieved by this optimization.
And, I'm wondering whether this optimization is also suitable to general
NUMA balancing or not.
