Linux – Understanding difference between system and process memory in htop

htoplinuxmemory

I'm a bit confused by the memory stats that htop is reporting on one of our servers. On the top bars, it's showing system memory as:

Mem: 456 / 7950MB

So, looks very low usage.

However, my main process is showing it's memory usage as:

VIRT    RES     SHR     MEM% 
13.3G   2388M   2239M   30%

Hmm, a lot higher.

Why are the system stats only showing 456MB used, when the process reports that it's using 2388MB?

Update Here's the output from free:

             total       used       free     shared    buffers     cached
Mem:       8141292    5425364    2715928          0     103560    4839368
-/+ buffers/cache:     482436    7658856
Swap:      2097148          0    2097148

Best Answer

Htop show memory: MEN TOTAL, USED, BUFFERS AND CACHE. If you sum used, buffers and cache you will have result equals result of command free. Htop you need to consider all results because process can use any memory. Man htop describe memory is:

   M_SIZE (VIRT)
        Size in memory of the total program size.

   M_SHARE (SHR)
        The size of the process’s shared pages

   PERCENT_MEM(MEN%)
        The percentage of memory the process is currently using (based on the process’s resident memory size, see M_RESIDENT below).

   M_RESIDENT (RES)
        The resident set size, i.e the size of the text and data sections, plus stack usage.

I hope I´ve helped.

Related Solutions

Linux – How to understand the memory usage and load average in linux server

(1) I see that each of the running processes occupies a very small percentage of memory (%MEM no more than 0.2%, and most just 0.0%), but how the total memory is almost used as in the fourth line of output ("Mem: 130766620k total, 130161072k used, 605548k free, 919300k buffers")? The sum of used percentage of memory over all processes seems unlikely to achieve almost 100%, doesn't it?

To see how much memory you are currently using, run free -m. It will provide output like:

             total       used       free     shared    buffers     cached
Mem:          2012       1923         88          0         91        515
-/+ buffers/cache:       1316        695
Swap:         3153        256       2896

The top row 'used' (1923) value will almost always nearly match the top row mem value (2012). Since Linux likes to use any spare memory to cache disk blocks (515).

The key used figure to look at is the buffers/cache row used value (1316). This is how much space your applications are currently using. For best performance, this number should be less than your total (2012) memory. To prevent out of memory errors, it needs to be less than the total memory (2012) and swap space (3153).

If you wish to quickly see how much memory is free look at the buffers/cache row free value (695). This is the total memory (2012)- the actual used (1316). (2012 - 1316 = 696, not 695, this will just be a rounding issue)

(2) how to understand the load average on the first line ("load average: 14.04, 14.02, 14.00")?

This article on load average uses a nice traffic analogy and is the best one I've found so far: Understanding Linux CPU Load - when should you be worried?. In your case, as people pointed out:

On multi-processor system, the load is relative to the number of processor cores available. The "100% utilization" mark is 1.00 on a single-core system, 2.00, on a dual-core, 4.00 on a quad-core, etc.

So, with a load average of 14.00 and 24 cores, your server is far from being overloaded.

What does monit consider to be memory usage

This could be get from the source of monit https://github.com/arnaudsj/monit/tree/master/process.

For linux the value is computed in sysdep_LINUX.c and comes from /proc/meminfo :

si->total_mem_kbyte = systeminfo.mem_kbyte_max - mem_free - buffers - cached;

In other words monit use as memory usage MemTotal - MemFree - Buffers - Cached.

In your case 998 - 146 - 114 - 70 = 668

Best Answer

Related Solutions

Linux – How to understand the memory usage and load average in linux server

What does monit consider to be memory usage

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