linux系统性能相关参数介绍
2016-09-19 13:54
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Linux系统cache的释放:
通过文件/proc/sys/vm/drop_caches来控制已使用内存的控制:
控制已经使用cache的释放方式:
drop_caches的详细文档如下:
Writing to this will cause the kernel to drop clean caches, dentries and inodes from memory, causing that memory to become free.
To free pagecache:
* echo 1 > /proc/sys/vm/drop_caches
To free dentries and inodes:
* echo 2 > /proc/sys/vm/drop_caches
To free pagecache, dentries and inodes:
* echo 3 > /proc/sys/vm/drop_caches
As this is a non-destructive operation, and dirty objects are notfreeable, the user should run “sync” first in order to make sure allcached objects are freed.
This tunable was added in 2.6.16.
该文件表示强制Linux VM最低保留多少空闲内存(Kbytes)。
缺省设置:724(512M物理内存)
该文件指定了内核针对内存分配的策略,其值可以是0、1、2。
0, 表示内核将检查是否有足够的可用内存供应用进程使用;如果有足够的可用内存,内存申请允许;否则,内存申请失败,并把错误返回给应用进程。
1, 表示内核允许分配所有的物理内存,而不管当前的内存状态如何。
2, 表示内核允许分配超过所有物理内存和交换空间总和的内存(参照overcommit_ratio)。
缺省设置:0
该文件表示,如果overcommit_memory=2,可以过载内存的百分比,通过以下公式来计算系统整体可用内存。
系统可分配内存=交换空间+物理内存*overcommit_ratio/100
该文件表示系统进行交换行为的程度,数值(0-100)越高,越可能发生磁盘交换。
该文件表示内核回收用于directory和inode cache内存的倾向
该文件表示在写一次到swap区的时候写入的页面数量,0表示1页,1表示2页,2表示4页。
缺省设置:3(2的3次方,8页)
关于page cache一些相关系统参数设置
vm.dirty_background_ratio:
is the percentage of system memory that can be filled with “dirty” pages — memory pages that still need to be written to disk — before the pdflush/flush/kdmflush background processes kick in to write it to disk. My example is 10%, so if my virtual server has 32 GB of memory that’s 3.2 GB of data that can be sitting in RAM before something is done.
vm.dirty_ratio:
is the absolute maximum amount of system memory that can be filled with dirty pages before everything must get committed to disk. When the system gets to this point all new I/O blocks until dirty pages have been written to disk. This is often the source of long I/O pauses, but is a safeguard against too much data being cached unsafely in memory.
vm.dirty_background_bytes & vm.dirty_bytes:
are another way to specify these parameters. If you set the _bytes version the _ratio version will become 0, and vice-versa.
vm.dirty_expire_centisecs:
is how long something can be in cache before it needs to be written. In this case it’s 30 seconds. When the pdflush/flush/kdmflush processes kick in they will check to see how old a dirty page is, and if it’s older than this value it’ll be written asynchronously to disk. Since holding a dirty page in memory is unsafe this is also a safeguard against data loss.
vm.dirty_writeback_centisecs:
is how often the pdflush/flush/kdmflush processes wake up and check to see if work needs to be done.
动态修改系统配置参数,立刻生效,但不具有持久性(系统重启就会丢失)
修改sysctl.conf系统配置文件,然后执行sysctl -p,重新加载生效,具有持久性:
通过文件/proc/sys/vm/drop_caches来控制已使用内存的控制:
控制已经使用cache的释放方式:
drop_caches的详细文档如下:
Writing to this will cause the kernel to drop clean caches, dentries and inodes from memory, causing that memory to become free.
To free pagecache:
* echo 1 > /proc/sys/vm/drop_caches
To free dentries and inodes:
* echo 2 > /proc/sys/vm/drop_caches
To free pagecache, dentries and inodes:
* echo 3 > /proc/sys/vm/drop_caches
As this is a non-destructive operation, and dirty objects are notfreeable, the user should run “sync” first in order to make sure allcached objects are freed.
This tunable was added in 2.6.16.
/proc/sys/vm/min_free_kbytes
该文件表示强制Linux VM最低保留多少空闲内存(Kbytes)。
缺省设置:724(512M物理内存)
/proc/sys/vm/overcommit_memory
该文件指定了内核针对内存分配的策略,其值可以是0、1、2。
0, 表示内核将检查是否有足够的可用内存供应用进程使用;如果有足够的可用内存,内存申请允许;否则,内存申请失败,并把错误返回给应用进程。
1, 表示内核允许分配所有的物理内存,而不管当前的内存状态如何。
2, 表示内核允许分配超过所有物理内存和交换空间总和的内存(参照overcommit_ratio)。
缺省设置:0
/proc/sys/vm/overcommit_ratio
该文件表示,如果overcommit_memory=2,可以过载内存的百分比,通过以下公式来计算系统整体可用内存。
系统可分配内存=交换空间+物理内存*overcommit_ratio/100
/proc/sys/vm/swapiness
该文件表示系统进行交换行为的程度,数值(0-100)越高,越可能发生磁盘交换。
/proc/sys/vm/vfs_cache_pressure
该文件表示内核回收用于directory和inode cache内存的倾向
/proc/sys/vm/page-cluster
该文件表示在写一次到swap区的时候写入的页面数量,0表示1页,1表示2页,2表示4页。
缺省设置:3(2的3次方,8页)
关于page cache一些相关系统参数设置
vm.dirty_background_ratio:
is the percentage of system memory that can be filled with “dirty” pages — memory pages that still need to be written to disk — before the pdflush/flush/kdmflush background processes kick in to write it to disk. My example is 10%, so if my virtual server has 32 GB of memory that’s 3.2 GB of data that can be sitting in RAM before something is done.
vm.dirty_ratio:
is the absolute maximum amount of system memory that can be filled with dirty pages before everything must get committed to disk. When the system gets to this point all new I/O blocks until dirty pages have been written to disk. This is often the source of long I/O pauses, but is a safeguard against too much data being cached unsafely in memory.
vm.dirty_background_bytes & vm.dirty_bytes:
are another way to specify these parameters. If you set the _bytes version the _ratio version will become 0, and vice-versa.
vm.dirty_expire_centisecs:
is how long something can be in cache before it needs to be written. In this case it’s 30 seconds. When the pdflush/flush/kdmflush processes kick in they will check to see how old a dirty page is, and if it’s older than this value it’ll be written asynchronously to disk. Since holding a dirty page in memory is unsafe this is also a safeguard against data loss.
vm.dirty_writeback_centisecs:
is how often the pdflush/flush/kdmflush processes wake up and check to see if work needs to be done.
动态修改系统配置参数,立刻生效,但不具有持久性(系统重启就会丢失)
$echo {parameters} /proc/sys/vm/{options} or $sysctl -w variable=value
修改sysctl.conf系统配置文件,然后执行sysctl -p,重新加载生效,具有持久性:
$vim /etc/sysctl.conf $sysctl -p
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