KVM内存管理（一）—— 设置基本参数

内存(Memory)是计算机的重要部件之一，也称内存储器和主存储器，它用于暂时存放CPU中的运算数据，与硬盘等外部存储器交换的数据。它是外存与CPU进行沟通的桥梁，计算机中所有程序的运行都在内存中进行，内存性能的强弱影响计算机整体发挥的水平。只要计算机开始运行，操作系统就会把需要运算的数据从内存调到CPU中进行运算，当运算完成，CPU将结果传送出来。

内存的运行也决定计算机整体运行快慢的程度。

 

内存设置基本参数

通过qemu命令行启动虚拟机时设置内存大小的参数如下：

-m [size=]megs[,slots=n,maxmem=size]
                configure guest RAM
                size: initial amount of guest memory
                slots: number of hotplug slots (default: none)
                maxmem: maximum amount of guest memory (default: none)

默认单位为MB，也支持加上“M” 或 “G”，分别代表MB、GB。

启动一个简单的虚拟机。

[root@localhost ~]# /usr/libexec/qemu-kvm -m 1024 centos70-64.qcow2 -serial stdio
VNC server running on ::1:5900


CentOS Linux 7 (Core)
Kernel 3.10.0-1127.el7.x86_64 on an x86_64

localhost login: root
Password: 
Last login: Thu Apr  1 07:37:56 on ttyS0
[root@localhost ~]# 
[root@localhost ~]# dmesg | grep -i memory
[    0.000000] Base memory trampoline at [ffff981380099000] 99000 size 24576
[    0.000000] crashkernel=auto resulted in zero bytes of reserved memory.
[    0.000000] Early memory node ranges
[    0.000000] PM: Registered nosave memory: [mem 0x0009f000-0x0009ffff]
[    0.000000] PM: Registered nosave memory: [mem 0x000a0000-0x000effff]
[    0.000000] PM: Registered nosave memory: [mem 0x000f0000-0x000fffff]
[    0.000000] Memory: 990828k/1048448k available (7784k kernel code, 392k absent, 57228k reserved, 5957k data, 1980k init)
[    0.000000] please try 'cgroup_disable=memory' option if you don't want memory cgroups
[    0.039135] Initializing cgroup subsys memory
[    0.524271] x86/mm: Memory block size: 128MB
[    2.276810] Freeing initrd memory: 20928k freed
[    2.431512] Non-volatile memory driver v1.3
[    2.432378] crash memory driver: version 1.1
[    2.487655] Freeing unused kernel memory: 1980k freed
[    2.509818] Freeing unused kernel memory: 396k freed
[    2.517783] Freeing unused kernel memory: 540k freed
[   16.928537] [TTM] Zone  kernel: Available graphics memory: 507350 kiB
[root@localhost ~]# 
[root@localhost ~]# cat /proc/meminfo 
MemTotal:        1014700 kB
MemFree:          803032 kB
MemAvailable:     778720 kB
Buffers:            2108 kB
Cached:            82836 kB
SwapCached:            0 kB
Active:            80076 kB
Inactive:          65072 kB
Active(anon):      60416 kB
Inactive(anon):     6576 kB
Active(file):      19660 kB
Inactive(file):    58496 kB
Unevictable:           0 kB
Mlocked:               0 kB
SwapTotal:        946172 kB
SwapFree:         946172 kB
Dirty:                 4 kB
Writeback:             0 kB
AnonPages:         60236 kB
Mapped:            22512 kB
Shmem:              6788 kB
Slab:              38448 kB
SReclaimable:      16140 kB
SUnreclaim:        22308 kB
KernelStack:        1728 kB
PageTables:         3872 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:     1453520 kB
Committed_AS:     298332 kB
VmallocTotal:   34359738367 kB
VmallocUsed:       26280 kB
VmallocChunk:   34359685116 kB
Percpu:              176 kB
HardwareCorrupted:     0 kB
AnonHugePages:      4096 kB
CmaTotal:              0 kB
CmaFree:               0 kB
HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
DirectMap4k:       63360 kB
DirectMap2M:      985088 kB
[root@localhost ~]#