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Apache 2.4.6 on Centos 7 is using 2gb memory sitting idle. The tail access log shows no usage, and it's not a public server.

ps aux --sort=-%mem | awk 'NR<=10{print $0}'

USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
apache   28363  0.3 41.7 2102448 1620940 ?     S    Apr16  16:38 /usr/sbin/httpd -DFOREGROUND
mysql      870  0.0  3.3 802388 129660 ?       Ssl  Apr05   8:23 /usr/sbin/mysqld
apache   30986  0.2  1.3 534800 51272 ?        S    Apr15  13:06 /usr/sbin/httpd -DFOREGROUND
apache   26210  0.1  0.8 516828 33788 ?        S    Apr18   2:16 /usr/sbin/httpd -DFOREGROUND
apache   31230  0.1  0.8 516208 31580 ?        S    Apr15   9:45 /usr/sbin/httpd -DFOREGROUND
apache   30141  0.1  0.6 505848 23752 ?        S    Apr16   4:04 /usr/sbin/httpd -DFOREGROUND
apache    1938  0.7  0.5 503100 21036 ?        S    Apr18   7:40 /usr/sbin/httpd -DFOREGROUND
apache   25774  0.5  0.5 421680 20888 ?        S    Apr18   6:39 /usr/sbin/httpd -DFOREGROUND
apache   25768  0.6  0.4 416716 15948 ?        S    Apr18   8:55 /usr/sbin/httpd -DFOREGROUND

free -m

              total        used        free      shared  buff/cache   available
Mem:           3789        1959         128         112        1701        1455
Swap:             0           0           0

It seems to point to a cache issue. The server runs 99.9% php scripts, so I don't know what it is even caching. The memory usage remains used indefinitely unless I restart apache.

The reason it's an issue is when I'm actually running scripts, the server runs out of memory. Any ideas why 2gb memory is used at idle?

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  • It's PHP using that memory. Apr 19, 2018 at 16:59
  • How is it using it? Cache, but it's not freeable? No scripts are running. How can I reduce it? Apr 20, 2018 at 16:26

1 Answer 1

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This is not a problem. Actual problems with Linux running low on memory are high page out to swap rates, allocstalls indicating direct reclaim, or the OOM killer.

You cannot, and do not want to, reduce caching. It speeds up I/O with unused memory, and will quickly give it up when user processes demand more. Both the operating system files and your applications will eventually be cached, which is why this seems large.

Standard explainer website: https://www.linuxatemyram.com/

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