In this tutorial, I have written about Linux understand Page cache and buffer cache in Linux System.
Most file-system cache data read from disk.
Linux understand Page cache
What does Page cache work?
A cache of data is accessed via the file system.
How to check page cache is actually used.
Create a large file
[root@DevopsRoles ~]# mkdir /test [root@DevopsRoles ~]# dd if=/dev/zero of=/test/large.txt count=100 bs=10M 100+0 records in 100+0 records out 1048576000 bytes (1.0 GB) copied, 1.62731 s, 644 MB/s [root@DevopsRoles ~]# echo 3 > /proc/sys/vm/drop_caches
Check memory usage before putting it in the page cache
[root@DevopsRoles ~]# vmstat procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu----- r b swpd free buff cache si so bi bo in cs us sy id wa st 1 0 0 377344 0 64336 0 0 441 5203 131 293 0 2 97 0 0 [root@DevopsRoles ~]# cat /test/large.txt > /dev/null
Check memory usage after getting on page cache
[root@DevopsRoles ~]# vmstat
procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
r b swpd free buff cache si so bi bo in cs us sy id wa st
2 0 0 6500 0 435008 0 0 3265 3008 108 179 0 2 98 0 0
We will confirm that accessing data in the cache is fast.
Run command 1s
[root@DevopsRoles ~]# time cat /test/large.txt > /dev/null
real 0m1.068s
user 0m0.003s
sys 0m0.987s
Run command 2s
[root@DevopsRoles ~]# time cat /test/large.txt > /dev/null
real 0m1.064s
user 0m0.003s
sys 0m0.981s
Linux understand buffer cache
What does Buffer cache work?
Cache data accessed via raw I/O. It is a page cache for block devices.
How to check Buffer cache is actually used.
[root@DevopsRoles ~]# vmstat procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu----- r b swpd free buff cache si so bi bo in cs us sy id wa st 1 0 0 5668 0 435832 0 0 6434 2087 116 132 0 2 98 0 0 [root@DevopsRoles ~]# dd if=/dev/sda of=/dev/null count=100 bs=10M 100+0 records in 100+0 records out 1048576000 bytes (1.0 GB) copied, 1.59043 s, 659 MB/s
Increase buffer cache (buff)
We will confirm that accessing data in the cache is fast.
Run command 1s
[root@DevopsRoles ~]# vmstat procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu----- r b swpd free buff cache si so bi bo in cs us sy id wa st 2 0 0 13408 359528 68520 0 0 7715 1888 123 127 0 2 98 0 0 [root@DevopsRoles ~]# time dd if=/dev/sda of=/dev/null count=100 bs=10M 100+0 records in 100+0 records out 1048576000 bytes (1.0 GB) copied, 1.13208 s, 926 MB/s real 0m1.138s user 0m0.001s sys 0m1.068s
Run command 2s
[root@DevopsRoles ~]# vmstat procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu----- r b swpd free buff cache si so bi bo in cs us sy id wa st 2 0 0 13664 359220 68520 0 0 8896 1747 130 119 0 2 98 0 0 [root@DevopsRoles ~]# time dd if=/dev/sda of=/dev/null count=100 bs=10M 100+0 records in 100+0 records out 1048576000 bytes (1.0 GB) copied, 1.13821 s, 921 MB/s real 0m1.144s user 0m0.001s sys 0m1.072s
Conclusion
Linux understand Page cache and buffer cache. I hope will this your helpful. Thank you for reading the DevopsRoles page!
