关于 Linux中缓存清理的一些笔记

空闲的物理内存的大小。

┌──[root@liruilongs.github.io]-[/proc/sys/vm]
└─$ man -K drop_caches
--Man-- next: proc(5) [ view (return) | skip (Ctrl-D) | quit (Ctrl-C) ]

drop_caches

Writing to this will cause the kernel to drop clean caches, as well as
reclaimable slab objects like dentries and inodes.  Once dropped, their
memory becomes free.

To free pagecache:
	echo 1 > /proc/sys/vm/drop_caches
To free reclaimable slab objects (includes dentries and inodes):
	echo 2 > /proc/sys/vm/drop_caches
To free slab objects and pagecache:
	echo 3 > /proc/sys/vm/drop_caches

This is a non-destructive operation and will not free any dirty objects.
To increase the number of objects freed by this operation, the user may run
`sync' prior to writing to /proc/sys/vm/drop_caches.  This will minimize the
number of dirty objects on the system and create more candidates to be
dropped.

This file is not a means to control the growth of the various kernel caches
(inodes, dentries, pagecache, etc...)  These objects are automatically
reclaimed by the kernel when memory is needed elsewhere on the system.

Use of this file can cause performance problems.  Since it discards cached
objects, it may cost a significant amount of I/O and CPU to recreate the
dropped objects, especially if they were under heavy use.  Because of this,
use outside of a testing or debugging environment is not recommended.

You may see informational messages in your kernel log when this file is
used:

	cat (1234): drop_caches: 3

These are informational only.  They do not mean that anything is wrong
with your system.  To disable them, echo 4 (bit 2) into drop_caches.

┌──(root💀Liruilong)-[/mnt/c/Users/lenovo]
└─# sync

┌──(root💀Liruilong)-[/mnt/c/Users/lenovo]
└─# free -m
               total        used        free      shared  buff/cache   available
Mem:           12480          84       12355           0          40       12228
Swap:           4096           0        4096

┌──(root💀Liruilong)-[/mnt/c/Users/lenovo]
└─# echo 3 > /proc/sys/vm/drop_caches

┌──(root💀Liruilong)-[/mnt/c/Users/lenovo]
└─# free -m
               total        used        free      shared  buff/cache   available
Mem:           12480          84       12372           0          23       12237
Swap:           4096           0        4096

To free pagecache:
	echo 1 > /proc/sys/vm/drop_caches
To free reclaimable slab objects (includes dentries and inodes):
	echo 2 > /proc/sys/vm/drop_caches
To free slab objects and pagecache:
	echo 3 > /proc/sys/vm/drop_caches

#!/bin/bash

#@File    :   clear.sh
#@Time    :   2021/12/27 23:52:20
#@Author  :   Li Ruilong
#@Version :   1.0
#@Desc    :   清除缓存的shell
#@Contact :   1224965096@qq.com


max=10000 # 缓存的最大值

clearLog=/var/log/clearfreelog
if [ ! -f $clearLog ];then
  touch $clearLog
fi

filesize=$(du -m  $clearLog | awk '{ print $1 }')
echo  "filesize=$filesize"
if [ $filesize -gt 300 ]; then
echo $clearLog
  > $clearLog
fi

cache=$( free -m | grep Mem | awk '{print $(NF-1)}')

time=$(date)


if [ $cache -gt $max ]
then
    echo "$time cache=$cache    flush cache start!" >> $clearLog
    sync
    echo  3 > /proc/sys/vm/drop_caches
    echo "$time FreeMemory Success!" >> $clearLog
else
    echo "$time cache=$cache  Memory is normal" >> $clearLog
fi