mm: multi-gen LRU: optimize multiple memcgs

mm: multi-gen LRU: optimize multiple memcgs

When multiple memcgs are available, it is possible to make better choices
based on generations and tiers and therefore improve the overall
performance under global memory pressure.  This patch adds a rudimentary
optimization to select memcgs that can drop single-use unmapped clean
pages first.  Doing so reduces the chance of going into the aging path or
swapping.  These two operations can be costly.

A typical example that benefits from this optimization is a server running
mixed types of workloads, e.g., heavy anon workload in one memcg and heavy
buffered I/O workload in the other.

Though this optimization can be applied to both kswapd and direct reclaim,
it is only added to kswapd to keep the patchset manageable.  Later
improvements will cover the direct reclaim path.

Server benchmark results:
  Mixed workloads:
    fio (buffered I/O): +[1, 3]%
                IOPS         BW
      patch1-8: 2154k        8415MiB/s
      patch1-9: 2205k        8613MiB/s

    memcached (anon): +[132, 136]%
                Ops/sec      KB/sec
      patch1-8: 819618.49    31838.48
      patch1-9: 1916516.06   74447.92

  Mixed workloads:
    fio (buffered I/O): +[59, 61]%
                IOPS         BW
      5.18-rc1: 1378k        5385MiB/s
      patch1-9: 2205k        8613MiB/s

    memcached (anon): +[229, 233]%
                Ops/sec      KB/sec
      5.18-rc1: 578946.00    22489.44
      patch1-9: 1916516.06   74447.92

  Configurations:
    (changes since patch 6)

    cat mixed.sh
    modprobe brd rd_nr=2 rd_size=56623104

    swapoff -a
    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

    fio -name=mglru --numjobs=36 --directory=/mnt --size=1408m \
      --buffered=1 --ioengine=io_uring --iodepth=128 \
      --iodepth_batch_submit=32 --iodepth_batch_complete=32 \
      --rw=randread --random_distribution=random --norandommap \
      --time_based --ramp_time=10m --runtime=90m --group_reporting &
    pid=$!

    sleep 200

    memtier_benchmark -S /var/run/memcached/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

Client benchmark results:
  no change (CONFIG_MEMCG=n)

Link: https://lkml.kernel.org/r/20220407031525.2368067-10-yuzhao@google.com
Signed-off-by: Yu Zhao <yuzhao@google.com>
Acked-by: Brian Geffon <bgeffon@google.com>
Acked-by: Jan Alexander Steffens (heftig) <heftig@archlinux.org>
Acked-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Acked-by: Steven Barrett <steven@liquorix.net>
Acked-by: Suleiman Souhlal <suleiman@google.com>
Tested-by: Daniel Byrne <djbyrne@mtu.edu>
Tested-by: Donald Carr <d@chaos-reins.com>
Tested-by: Holger Hoffstätte <holger@applied-asynchrony.com>
Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
Tested-by: Shuang Zhai <szhai2@cs.rochester.edu>
Tested-by: Sofia Trinh <sofia.trinh@edi.works>
Tested-by: Vaibhav Jain <vaibhav@linux.ibm.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Will Deacon <will@kernel.org>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>