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.
And yes, this:
sysctl -w vm.max_map_count=65535
is just a nicer way of writing this:
echo 65535 > /proc/sys/vm/max_map_count