OpenVZ VPS memory optimisation

This article shows techniques used to trim memory usage on OpenVZ system (with 128 MB RAM burstable). Mostly inspired by this article from lowendbox.com.

Minimal Debian Lenny install (33MB used):

# ps xo vsz,rsz,ucmd
VSZ    RSZ CMD
1980   692 init
26988  1236 rsyslogd
5272  1024 sshd
2036   792 cron
8016  2916 sshd
4324  1632 bash
3604   804 ps
# free -m
total       used       free     shared    buffers     cached
Mem:           128         33         95          0          0          0
-/+ buffers/cache:         33         95
Swap:            0          0          0

After setting "ulimit -s 128" in /etc/init.d/rc (9MB used):

# ps xo vsz,rsz,ucmd
VSZ    RSZ CMD
1980   692 init
2744  1188 rsyslogd
5272  1020 sshd
2036   792 cron
8016  2888 sshd
4324  1628 bash
3604   804 ps

# free -m
total       used       free     shared    buffers     cached
Mem:           128          9        118          0          0          0
-/+ buffers/cache:          9        118
Swap:            0          0          0

Next operation: replace rsyslogd with syslog-ng (still 9 MB used):

# ps xo vsz,rsz,ucmd
   VSZ   RSZ CMD
  1980   688 init
  5272  1040 sshd
  2036   792 cron
  2848   748 syslog-ng
  8016  2892 sshd
  4360  1712 bash
  3604   808 ps

# free -m
             total       used       free     shared    buffers     cached
Mem:           128          9        118          0          0          0
-/+ buffers/cache:          9        118
Swap:            0          0          0

I replaced bash with dash (smaller memory usage). Free memory remains the same (we keep bash for root interactive login). Bigger benefits come from using dropbear instead of sshd:

# ps xo vsz,rsz,ucmd
   VSZ   RSZ CMD
  1980   688 init
  2036   792 cron
  2848   748 syslog-ng
  2040   468 dropbear
  2700  1240 dropbear
  2788  1512 bash
  2084   704 ps

# free -m
             total       used       free     shared    buffers     cached
Mem:           128          4        123          0          0          0
-/+ buffers/cache:          4        123
Swap:            0          0          0

Yes! we're using only 4MB of VSZ now!.

Next, we would like to install a database, MySQL is a most popular choice here:

# ps xao vsz,rsz,ucmd
   VSZ   RSZ CMD
  1980   688 init
  2036   792 cron
  2848   808 syslog-ng
  2040   468 dropbear
  2700  1332 dropbear
  2796  1564 bash
  1704   516 mysqld_safe
 62440 17968 mysqld
  1628   532 logger
  2084   700 ps

# free -m
             total       used       free     shared    buffers     cached
Mem:           128         61         66          0          0          0
-/+ buffers/cache:         61         66
Swap:            0          0          0

Pretty fat. Let's remove innodb support first:

# ps xao vsz,rsz,ucmd
   VSZ   RSZ CMD
  1980   688 init
  2036   792 cron
  2848   808 syslog-ng
  2040   468 dropbear
  2700  1332 dropbear
  2804  1572 bash
  1704   516 mysqld_safe
 44648  7208 mysqld
  1628   532 logger
  2084   700 ps

# free -m
             total       used       free     shared    buffers     cached
Mem:           128         43         84          0          0          0
-/+ buffers/cache:         43         84
Swap:            0          0          0

After applying minimal settings on my.conf file:

# ps xao vsz,rsz,ucmd
   VSZ   RSZ CMD
  1980   688 init
  2036   792 cron
  2848   808 syslog-ng
  2040   468 dropbear
  2700  1332 dropbear
  2804  1572 bash
  1704   516 mysqld_safe
 28256  5320 mysqld
  1628   532 logger
  2084   708 ps

# free -m
             total       used       free     shared    buffers     cached
Mem:           128         27        100          0          0          0
-/+ buffers/cache:         27        100
Swap:            0          0          0

Now lightpd installation:

# ps xao vsz,rsz,ucmd
   VSZ   RSZ CMD
  1980   688 init
  2036   792 cron
  2848   808 syslog-ng
  2040   468 dropbear
  2700  1332 dropbear
  2804  1572 bash
  1704   516 mysqld_safe
 28256  5320 mysqld
  1628   532 logger
  1764   512 portmap
  3136   504 famd
  5408  1004 lighttpd
  2084   704 ps

# free -m
total       used       free     shared    buffers     cachedMem:           128         28         99          0          0          0
-/+ buffers/cache:         28         99
Swap:            0          0          0

Not bad. 28 MB used so far.

UPDATE: I found interesting article on optimizing MySQL and added the following options:

query_cache_size = 50K
query_cache_limit = 50K

Memory usage after change:

# ps xao vsz,rsz,ucmd
VSZ   RSZ CMD
1980   688 init
1764   512 portmap
2796  1248 rsyslogd
5404  1008 lighttpd
3136   500 famd
2036   796 cron
2040   468 dropbear
2696  1340 dropbear
2804  1576 bash
1704   516 mysqld_safe
11436  5112 mysqld
1628   532 logger
2084   700 ps

# free -m
total       used       free     shared    buffers     cached
Mem:           128         12        115          0          0          0
-/+ buffers/cache:         12        115
Swap:            0          0          0

12 MB VSZ with lightpd and MySQL! 🙂

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One Response to OpenVZ VPS memory optimisation

  1. satyricon says:

    nice but unusable

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