You definitely seem to have a memory leak, but there is no information in your report which might give a clue as to what is leaking and whether it may already be fixed.,
As well as providing version information and information about how you use Asterisk, you should also consider building with MALLOC_DEBUG and the use of valgrind.
The memory leak increment and what is happening at the time of increments is likely to be useful.
I was working on it for more than 6 months, this is not a memory cache issue and you CANNOT fix it by “sync; echo 3 > /proc/sys/vm/drop_caches”. It’s only the kernel issue that fixed in kernel 4.x lt. So you can use this instruction for upgrade your kernel: https://www.tecmint.com/install-upgrade-kernel-version-in-centos-7/
I hope it will be helpful everyone has this issue.