How much memory could vm use

Question

I read the document Understanding Virtual Memory and it said one method for changing tunable parameters in the Linux VM was the command:

sysctl -w vm.max_map_count=65535

I want to know what the number 65535 means and how much memory could vm use by the setting.

Answer 1

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

Answer 2

echo 'vm.max_map_count=262144' >> /etc/sysctl.conf

sysctl -p

Answer 3

echo "vm.max_map_count=262144" >> /etc/sysctl.conf
sysctl -p

This does not work since we cannot change the configuration file directly. Run the below command.

echo vm.max_map_count=262144 | sudo tee -a /etc/sysctl.conf

But check if vm.max_map_count already exists or not. You can do that using

grep vm.max_map_count /etc/sysctl.conf