How to see memory usage history

A complete re-write of my previous post. Got a bit curious and checked out further.

In short: the reason for the difference is that openSUSE uses a patched version of top and free that adds some extra values to `cached'.

A) Standard version

top, free, htop, ...:

Usage is calculated by reading data from /proc/meminfo:

E.g.:

#free:
Row   Column  | Corresponding /proc/meminfo entry
-----|--------|----------------------------------
Mem:

      total   : MemTotal
      used    : MemTotal - MemFree
      free    : MemFree
      shared  : MemShared
      buffers : Buffers
      cached  : Cached
-----|--------|----------------------------------
-/+ buffers/cache:

      used    : (MemTotal - MemFree) - (Buffers + Cached)
      free    :  MemFree             + (Buffers + Cached)

#htop:
    Used U*   : ((MemTotal - MemFree) - (Buffers + Cached)) / 1024

^*_{I'm using the name Used U for memory used by User Mode. Aka Used minus (Cached + Buffers).}

So in reality same calculation is used.

htop display the following in the memory meter:

[Used U % of total | Buffers % of total | Cached % of total ] UsedU MB

(MB is actually MiB.)

B) Patched version

The base for free and top on Debian, Fedora, openSuse is is procps-ng. However, each flavour add their own patches that might, or migh not become part of the main project.

Under openSUSE we find various additions to the top/free (procps) package. The ones to take notice of here is some additional values used to represent the cache value. (I did not include these in my previous post as my system uses a "clean" procps.)

B.1) Additions

In /proc/meminfo we have Slab which is in-kernel data structure cache. As a sub category we find SReclaimable which is part of Slab that might be reclaimed for other use both by Kernel and User Mode.

Further we have SwapCached which is memory that once was swapped out, is swapped in but also is in the swap-file. Thus if one need to swap it out again, this is already done.

Lastly there is NFS_Unstable which are pages sent to the server but not yet committed to stable storage.

The following values are added to cache in the openSUSE patched version:

SReclaimable
SwapCached
NFS_Unstable

(In addition there are some checks that total has to be greater then free, used has to be greater then buffers + cache etc.)

B.2) Result

Looking at free, as a result the following values are the same: total, used, free and buffers.

The following are changed: cached and "+/- buffers".

used    = MemTotal - MemFree

old:
    cached         : Cached
    +-/buffers-used: used - (Buffers + Cached)
    +/-buffers-free: free + (Buffers + Cached)

patched:
    cached         : Cached + SReclaimable + SwapCached + NFS_Unstable
    +/-buffers-used: used - (Buffers + Cached + SReclaimable +
                     SwapCached + NFS_Unstable)
    +/-buffers-free: free + (Buffers + Cached + SReclaimable +
                     SwapCached + NFS_Unstable)

The same additions are done to top.

htop is unchanged and thus only aligning with older / or un-patched versions of top / free.

Here's what I've done to 'solve' it:

1. Set MaxClients 7 (based on (1740.8Mb Memory on server - 900Mb for MySQL + other stuff) / 111Mb average usage per httpd process = 7.5747747747747747747747747747748)

Therefore:

<IfModule prefork.c>
StartServers       8
MinSpareServers    5
MaxSpareServers   20
ServerLimit      256
MaxClients         7
MaxRequestsPerChild  4000
</IfModule>

2. Disable all Apache modules except for authz_host_module, log_config_module, expires_module, deflate_module, setenvif_module, mime_module, autoindex_module, negotiation_module, dir_module, alias_module, rewrite_module, php5_module

3. Remove the mod_ssl package since the client isn't using https:// whatsoever.

I'll report back once this new configuration has been running a while to see if this solves it.

Some inspiration here was borrowed from: http://www.activoinc.com/blog/2009/08/31/performance-optimized-httpd-conf-for-magento-ecommerce/ and http://www.activoinc.com/downloads/httpd.conf-magento