There are some situations where you can somewhat handle malloc returning NULL.

One would be where you have frequent large mallocs which get freed fast. Another would be where you have written a garbage collected language in C/C++.

When calling free, delete or letting your GC do that for you the memory isn't actually given back immediately, glibc has malloc_trim(0) for that, which tries it's best to give back as much unused memory to the OS as possible.

Then you can retry your call to malloc and see if it fails and then just let your supervisor restart your service/host/whatever or not.