Add tips on swap (cyberbotics#5825)

* tips swap

* typo

* title

* style

* style

* test

* test

* test

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* typo

* Update docs/guide/advanced-configuration.md

Co-authored-by: Olivier Michel <Olivier.Michel@cyberbotics.com>

* Update docs/guide/advanced-configuration.md

Co-authored-by: Olivier Michel <Olivier.Michel@cyberbotics.com>

---------

Co-authored-by: Olivier Michel <Olivier.Michel@cyberbotics.com>

Author: Benjamin Délèze

docs/guide/advanced-configuration.md

@@ -93,3 +93,45 @@ To work, your assets folder must correspond to the version of Webots that is in
 For more informations about assets, see [here](installation-procedure.md#asset-cache-download).
 
 **Note**: This is already implemented in the Docker images provided by Cyberbotics.
+
+#### Increase the Number of Parallel Simulations Supported by the Server
+
+The server can become saturated because both its CPU and GPU RAM are full.
+What happens normally is that the GPU and CPU will grow in parallel as new simulations are added.
+In most cases the GPU RAM will be saturated first.
+Once it happens, the CPU RAM will take the share of the GPU and therefore fill up faster.
+Once the CPU RAM is full, the swap will take over.
+Once the swap is full, the computer will crash if we try to open more simulations.
+
+##### Enable the Zram
+
+[Zram](https://en.wikipedia.org/wiki/Zram) is a Linux kernel module that will compress the least used parts of the RAM.
+It has the same role as swap but is normally faster.
+
+To enable it:
+```
+sudo apt-get install zram-config
+sudo service zram-config start
+```
+
+To check the zram installation:
+```
+cat /proc/swaps
+```
+
+It should display something like:
+```
+Filename                                Type        Size    Used   Priority
+/dev/sda3                               partition   9215996 0      -1
+/dev/zram0                              partition   755740  8104    5
+/dev/zram1                              partition   755740  8004    5
+/dev/zram2                              partition   755740  8120    5
+/dev/zram3                              partition   755740  8064    5
+```
+
+#### Increase the Size of the Swap
+
+Increasing the size of the swap will allow the server to support more simulations in parallel.
+However, when the swap is filling-up, you may observe a performance drop.
+
+You can follow [this tutorial](https://linuxhandbook.com/increase-swap-ubuntu/) to increase the size of the swap.