From the Linux kernel documentation:
max_map_count:
This file contains the maximum number of memory map areas a process may have. Memory map areas are used as a side-effect of calling malloc, directly by mmap and mprotect, and also when loading shared libraries.
While most applications need less than a thousand maps, certain programs, particularly malloc debuggers, may consume lots of them, e.g., up to one or two maps per allocation.
The default value is 65536.
Bottom line: this setting limits the number of discrete mapped memory areas - on its own it imposes no limit on the size of those areas or on the memory that is usable by a process.
From stackoverflow: It does not determine directly how much memory a process can use. A process can allocate memory let's say in 64Kb chunks or 256Kb chunks, having 4x different total memory used. vm.max_map_count controls only number of these chunks.
I don't understand it clearly yet.
Side Effect when increasing vm.max_map_count https://www.novell.com/support/kb/doc.php?id=7000830