How can I deliberately reduce free memory in linux by a given amount? [closed] - linux

Question

Closed. This question does not meet Stack Overflow guidelines. It is not currently accepting answers.
We don’t allow questions seeking recommendations for books, tools, software libraries, and more. You can edit the question so it can be answered with facts and citations.
Closed 6 years ago.
Improve this question
I am looking for a quick and dirty way to analyze how a memory intensive third party application behaves under reduced memory conditions and determine a "minimum viable free memory" threshold.
you#yours:~$ free
total used free shared buffers cached
Mem: 993M 879M 113M 1.1M 15M 116M
you#yours:~$ hogMem 100 &
you#yours:~$ free
total used free shared buffers cached
Mem: 993M 979M 13M 1.1M 15M 116M
you#yours:~$ date; runTheThing; date;
you#yours:~$ fg
you#yours:~$ ^C
you#yours:~$ free
total used free shared buffers cached
Mem: 993M 879M 113M 1.1M 15M 116M
In the above, what could I use for hogMem?
I hope to do it with existing commands, without getting into a complicated programming problem. Googling this issue gets me 1,000s of pages about how to get more free memory, not less.
Update 2016/04/28 :
So, I found a super convenient way to do this, thanks to the hint by #Cyrus
you#yours:~$ sudo mkdir -p /media/temporary_ram_disk
you#yours:~$ sudo mount -t tmpfs -o size=2048M tmpfs /media/temporary_ram_disk/
you#yours:~$ sudo chown you:you /media/temporary_ram_disk/
you#yours:~$ cd /media/temporary_ram_disk/
you#yours:/media/temporary_ram_disk$ free -h
total used free shared buffers cached
Mem: 993M 879M 113M 1.1M 15M 116M
you#yours:/media/temporary_ram_disk$ fallocate -l 100M empty_file_100M
you#yours:/media/temporary_ram_disk$ ls -l
total 5120
-rw-r--r-- 1 you you 5242880 Apr 28 12:05 empty_file_100M
you#yours:/media/temporary_ram_disk$ free -h
total used free shared buffers cached
Mem: 993M 879M 13M 1.1M 15M 116M
So the hogMem I'm using is in fact fallocate !

Answer 1

Probably the best way to see "how a memory intensive third party application behaves under reduced memory conditions," is to run it under reduced memory conditions. On linux, this is easily done with prlimit.
For example, to see how date runs with its address space limited to 1,000,000 bytes, run:
$ prlimit -v1000000 date
Segmentation fault
To see how it runs with its address space limited to 10,000,000 bytes, run:
$ prlimit -v10000000 date
Wed Apr 27 12:00:13 PDT 2016
It is also possible to limit the target program's access to many other resources. For example the maximum number of open files or the maximum CPU time can also be limited.
prlimit is included in the util-linux package. For more details on its operation, see man prlimit.