drop_caches Linux清空缓存

drop_caches
Writing to this will cause thekernel to drop clean caches, dentries and
inodes from memory, causing thatmemory to become free.
To free pagecache:
         echo1 > /proc/sys/vm/drop_caches
To free dentries and inodes:
         echo2 > /proc/sys/vm/drop_caches
To free pagecache, dentries andinodes:
         echo3 > /proc/sys/vm/drop_caches
As this is a non-destructiveoperation and dirty objects are not freeable, the
user should run `sync' first.
http://www.kernel.org/doc/Documentation/sysctl/vm.txt

注意：在清空缓存之前使用sync命令同步数据到磁盘

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# cat /proc/sys/vm/drop_caches

0

默认是0，1表示清空页缓存，2表示清空inode和目录树缓存，3清空所有的缓存

# sync
# free -m
                     total       used       free     shared    buffers     cached
Mem:           499        323        175          0         52                188
-/+ buffers/cache:       82        416
Swap:         2047          0       2047
# echo 3 > /proc/sys/vm/drop_caches
# free -m     //发现缓存明显减少了
                    total       used       free     shared    buffers     cached
Mem:           499         83         415          0          1                17
-/+ buffers/cache:      64        434
Swap:         2047          0       2047
#
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