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.
3 Answers
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
echo 'vm.max_map_count=262144' >> /etc/sysctl.conf
sysctl -p
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
