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8.3.2. KSM 调整服务

ksmtuned 服务通过循环和调整 ksm，对内核相同的页面合并(KSM)配置进行微调。另外，当创建虚拟机或销毁时，libvirt 会通知 ksmtuned 服务。ksmtuned 服务没有选项。 
# systemctl start ksmtuned
Starting ksmtuned:                                         [  OK  ]
可以使用 retune 参数调优 ksmtuned 服务，该参数指示 ksmtuned 手动运行调优功能。
/etc/ksmtuned.conf 文件是 ksmtuned 服务的配置文件。下面的文件输出是默认的 ksmtuned.conf 文件： 
# Configuration file for ksmtuned.
# How long ksmtuned should sleep between tuning adjustments
# KSM_MONITOR_INTERVAL=60

# Millisecond sleep between ksm scans for 16Gb server.
# Smaller servers sleep more, bigger sleep less.
# KSM_SLEEP_MSEC=10

# KSM_NPAGES_BOOST - is added to the `npages` value, when `free memory` is less than `thres`.
# KSM_NPAGES_BOOST=300

# KSM_NPAGES_DECAY - is the value given is subtracted to the `npages` value, when `free memory` is greater than `thres`.
# KSM_NPAGES_DECAY=-50

# KSM_NPAGES_MIN - is the lower limit for the `npages` value.
# KSM_NPAGES_MIN=64

# KSM_NPAGES_MAX - is the upper limit for the `npages` value.
# KSM_NPAGES_MAX=1250

# KSM_THRES_COEF - is the RAM percentage to be calculated in parameter `thres`.
# KSM_THRES_COEF=20

# KSM_THRES_CONST - If this is a low memory system, and the `thres` value is less than `KSM_THRES_CONST`, then reset `thres` value to `KSM_THRES_CONST` value.
# KSM_THRES_CONST=2048

# uncomment the following to enable ksmtuned debug information
# LOGFILE=/var/log/ksmtuned
# DEBUG=1
在 /etc/ksmtuned.conf 文件中，npages 设置 ksm 在 ksm d 守护进程变为 inactive 之前将扫描多少页。这个值也会在 /sys/kernel/mm/ksm/pages_to_scan 文件中设置。
KSM_THRES_CONST 值代表激活 ksm 的可用内存量。如果发生以下情况之一，则激活 ksmd ：
  • 可用内存量低于阈值，在 KSM_THRES_CONST 中设置。
  • 所提交的内存量加上阈值 KSM_THRES_CONST 超过总内存量。