Memory

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Quick Understanding on swap

Swap Space is virtual memory, using your HDD when you run out of memory. The system swaps some of the contents out of the RAM to the HDD (swap), then bring it back when required.

In the past, when RAM was very small in the single digit of GB or less, we take the rule of 2 times the memory. But with large memory available in your Server, it may not be necessary to configure as much, as we only need as much as we can suspend to disk. I like to use between 16GB to 32GB swap

To control the tendency for the system to use the swap. Configure the vm.swappiness at /etc/sysctl.conf. It is the percentage of memory free before using swap. If you have lots of memory, you can use it as low as 10 from the default 60.

Do take a look at Quick Understanding on Swap

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Another way to calculate shared memory swapping

Using ipcs utlities to find out information on shared memory utilisation which can be useful for analysing the performance of the system. Let’s says you want to measure how much memory has been swapped.

% ipcs -mu
------ Shared Memory Status --------
segments allocated 55
pages allocated 6655333
pages resident  5661034
pages swapped   947522
Swap performance: 0 attempts     0 successes

where
-m is “information about active shared memory segments”
-u is “Show status summary”

You would need PAGE Memory

getconf PAGESIZE
4096

To provide us with the information in MB

echo "$((947522*4096/1024/1024)) MB"
3701 MB
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Opening the Door to Big Memory

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