Re: [PATCH v7 00/12] Multigenerational LRU Framework

Yu Zhao
2022-02-12T21:01:32Z

On Sat, Feb 12, 2022 at 05:12:19AM +0900, Alexey Avramov wrote:
> Aggressive swapping even with vm.swappiness=1 with MGLRU
> ========================================================
>
> Reading a large mmapped file leads to a super agressive swapping.
> Reducing vm.swappiness even to 1 does not have effect.

Mind explaining why you think it's "super agressive"? I assume you
expected a different behavior that would perform better. If so,
please spell it out.

> Demo: https://www.youtube.com/watch?v=J81kwJeuW58
>
> Linux 5.17-rc3, Multigenerational LRU v7,
> vm.swappiness=1, MemTotal: 11.5 GiB.
>
> $ cache-bench -r 35000 -m1 -b1 -p1 -f test20000
> Reading mmapped file (file size: 20000 MiB)
> cache-bench v0.2.0: https://github.com/hakavlad/cache-bench

Writing your own benchmark is a good exercise but fio is the standard
benchmark in this case. Please use it with --ioengine=mmap.

> Swapping started with MemAvailable=71%.
> At the end 33 GiB was swapped out when MemAvailable=60%.
>
> Is it OK?

MemAvailable is an estimate (free + page cache), and it doesn't imply
any reclaim preferences. In the worst case scenario, e.g., out of swap
space, MemAvailable *may* be reclaimed.

Here is my benchmark result with file mmap + *high* swap usage. Ram
disk was used to reduce the variance in the result (and SSD wear out
if you care). More details on additional configurations here:
https://lore.kernel.org/linux-mm/20220208081902.3550911-6-yuzhao@google.com/

Mixed workloads:
fio (buffered I/O): +13%
IOPS BW
5.17-rc3: 275k 1075MiB/s
v7: 313k 1222MiB/s

memcached (anon): +12%
Ops/sec KB/sec
5.17-rc3: 511282.72 19861.04
v7: 572408.80 22235.49

cat mmap.sh
systemctl restart memcached
swapoff -a
umount /mnt
rmmod brd

modprobe brd rd_nr=2 rd_size=56623104

mkswap /dev/ram0
swapon /dev/ram0

mkfs.ext4 /dev/ram1
mount -t ext4 /dev/ram1 /mnt

memtier_benchmark -S /var/run/memcached/memcached.sock \
-P memcache_binary -n allkeys --key-minimum=1 \
--key-maximum=50000000 --key-pattern=P:P -c 1 \
-t 36 --ratio 1:0 --pipeline 8 -d 2000

sysctl vm.overcommit_memory=1

fio -name=mglru --numjobs=36 --directory=/mnt --size=1408m \
--buffered=1 --ioengine=mmap --iodepth=128 --iodepth_batch_submit=32 \
--iodepth_batch_complete=32 --rw=randread --random_distribution=random \
--norandommap --time_based --ramp_time=10m --runtime=990m \
--group_reporting &
pid=$!

sleep 200

memcached.sock -P memcache_binary -n allkeys --key-minimum=1 \
--key-maximum=50000000 --key-pattern=R:R -c 1 -t 36 --ratio 0:1 \
--pipeline 8 --randomize --distinct-client-seed

kill -INT $pid
wait