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设置/ proc / sys / vm / drop_caches清除缓存

作为一些冷缓存时间的一部分,我试图释放OS缓存。 内核文档(于2019年1月检索) 表示:

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 3) into drop_caches.

我对细节有些粗略。跑步

echo 3 > /proc/sys/vm/drop_caches

释放页面缓存,牙科和索引节点。好。

因此,如果我希望系统再次正常开始缓存,是否需要先将其重置为0?我的系统当前将值设置为0,我认为这是默认值。还是会自行重置?我在这里至少看到两种可能性,但我不确定哪一种是正确的:

  1. echo 3 > /proc/sys/vm/drop_caches释放页面缓存,牙科和inode。然后,系统立即再次开始缓存。我不确定在这种情况下我希望/proc/sys/vm/drop_caches中的值做什么。几乎立即回到0?

  2. 如果/proc/sys/vm/drop_caches设置为3,则系统将不进行任何内存缓存,直到将其重置为0。

哪种情况是正确的?

89
Faheem Mitha

它不是粘性的-您只需写入文件以使其失去缓存,然后立即开始再次缓存。

基本上,当您写入该文件时,您实际上并没有更改设置,而是向内核发出命令。内核对该命令起作用(通过删除高速缓存),然后像以前一样进行。

114
TomH