Linux SWAP memory used when RAM is used by Kernel Buffer and Cache

Question

In some our servers (Suze and RedHat 7 / HP 460c with 128Go or RAM) the free RAM space is close to 0 due to a high usage of buffer and cache.

The cache and buffer memory is filled up during backup with symantec networker.

As buffer and cache are freeable memory (as far as I know), I was not worried about that and if the applications needs more memory space the kernel will free buffer and cache to get new RAM Space.

But, I was suprised to see that some times ago, the kernel were useing the SWAP... Could someone explain to me what could be the reasons that the kernel did not free RAM from buffer/cache to avoid using SWAP?

Regards

Maximilien

Answer 1

Here is one important thing : some times ago, we don't have such large RAM as now. So we need to use vritual memory for saving (also for other reasons like safe), and we use SWAP and do_page_fault() too.

With the development of RAM, we don't need to foucs on how to save the use of RAM. Instead, we foucs on how to speed up the access to hard disk by using RAM as a chache, that is why we use Buffer and Cache now.