Ygtjki

You can write a C program to malloc() the required memory and then use mlock() to prevent the memory from being swapped out.

Then just let the program wait for keyboard input, and unlock the memory, free the memory and exit.

I would suggest running a VM with limited memory and testing the software in that would be a more efficient test than trying to fill memory on the host machine.

That method also has the advantage that if the low memory situation causes OOM errors elsewhere and hangs the whole OS, you only hang the VM you are testing in not your machine that you might have other useful processes running on.

Also if your testing is not CPU or IO intensive, you could concurrently run instances of the tests on a family of VMs with a variety of low memory sizes.

From this HN comment: https://news.ycombinator.com/item?id=6695581

Just fill /dev/shm via dd or similar.

swapoff -a
dd if=/dev/zero of=/dev/shm/fill bs=1k count=1024k

1. run linux;


2. boot with mem=nn[KMG] kernel boot parameter

(look in linux/Documentation/kernel-parameters.txt for details).

If you have basic GNU tools (sh, grep, yes and head) you can do this:

yes | tr \n x | head -c $BYTES | grep n
# Protip: use `head -c $((1024*1024*2))` to calculate 2MB easily

This works because grep loads the entire line of data in RAM (I learned this in a rather unfortunate way when grepping a disk image). The line, generated by yes, replacing newlines, will be infinitely long, but is limited by head to $BYTES bytes, thus grep will load $BYTES in memory. Grep itself uses like 100-200KB for me, you might need to subtract that for a more precise amount.

If you want to also add a time constraint, this can be done quite easily in bash (will not work in sh):

cat <(yes | tr \n x | head -c $BYTES) <(sleep $NumberOfSeconds) | grep n

The <(command) thing seems to be little known but is often extremely useful, more info on it here: http://tldp.org/LDP/abs/html/process-sub.html

Then for the use of cat: cat will wait for inputs to complete until exiting, and by keeping one of the pipes open, it will keep grep alive.

If you have pv and want to slowly increase RAM use:

yes | tr \n x | head -c $BYTES | pv -L $BYTESPERSEC | grep n

For example:

yes | tr \n x | head -c $((1024*1024*1024)) | pv -L $((1024*1024)) | grep n

Will use up to a gigabyte at a rate of 1MB per second. As an added bonus, pv will show you the current rate of use and the total use so far. Of course this can also be done with previous variants:

yes | tr \n x | head -c $BYTES | pv | grep n

Just inserting the | pv | part will show you the current status (throughput and total, by default, I think - otherwise see the man(ual) page).

Why another answer? The accepted answer recommends installing a package (I bet there's a release for every chipset without needing a package manager); the top voted answer recommends compiling a C program (I did not have a compiler or toolchain installed to compile for your target platform); the second top voted answer recommends running the application in a VM (yeah let me just dd this phone's internal sdcard over usb or something and create a virtualbox image); the third suggests modifying something in the boot sequence which does not fill the RAM as desired; the fourth only works in so far as the /dev/shm mountpoint (1) exists and (2) is large (remounting needs root); the fifth combines many of the above without sample code; the sixth is a great answer but I did not see this answer before coming up with my own approach, so I thought I'd add my own, also because it's shorter to remember or type over if you don't see that the memblob line is actually the crux of the matter; the seventh again does not answer the question (uses ulimit to limit a process instead); the eighth tries to get you to install python; the ninth thinks we're all very uncreative and finally the tenth wrote his own C++ program which causes the same issue as the top voted answer.

I keep a function to do something similar in my dotfiles. https://github.com/sagotsky/.dotfiles/blob/master/.functions#L248

function malloc() awk 'print int($2/10)')
 if [[ $N -gt $1 ]] ;then 
 N=$1
 fi
 sh -c "MEMBLOB=$(dd if=/dev/urandom bs=1MB count=$N) ; sleep 1"
 fi

How abount a simple python solution?

#!/usr/bin/env python

import sys
import time

if len(sys.argv) != 2:
 print "usage: fillmem <number-of-megabytes>"
 sys.exit()

count = int(sys.argv[1])

megabyte = (0,) * (1024 * 1024 / 8)

data = megabyte * count

while True:
 time.sleep(1)

How about ramfs if it exists? Mount it and copy over a large file?
If there's no /dev/shm and no ramfs - I guess a tiny C program that does a large malloc based on some input value? Might have to run it a few times at once on a 32 bit system with a lot of memory.

If you want to test a particular process with limited memory you might be better off using ulimit to restrict the amount of allocatable memory.

I think this is a case of asking the wrong question and sanity being drowned out by people competing for the most creative answer. If you only need to simulate OOM conditions, you don't need to fill memory. Just use a custom allocator and have it fail after a certain number of allocations. This approach seems to work well enough for SQLite.

I wrote this little C++ program for that: https://github.com/rmetzger/dynamic-ballooner

The advantage of this implementation is that is periodically checks if it needs to free or re-allocate memory.