Re: Finding a user space alternative to the (removed) OOM killer

[Marcelo Tosatti <marcelo.tosatti@cyclades.com>]

On Mon, 22 Dec 2003, Anders Torger wrote:

> It has come to my attention that the OOM killer has been removed. I used it
> actively in my software in a hackish fashion, in the following way:
>
> I have implemented a reverb processor using convolution running on a compact
> linux platform, using no swap memory. In the setup process, there is a
> benchmarking algorithm that finds out through a series of test runs how short
> I/O delay (cpu limited) and how long reverb tails (memory limited) the
> computer can handle. The ugly (or elegant) hack here was to set the convolver
> process to user nobody and a nicer priority when it allocates its convolution
> buffers (can be more than hundred megabytes), which then will get it killed
> by the OOM killer if it runs out of memory, which is detected and treated by
> supporting code as it ran out of memory. All memory is touched by memset and
> an temporary dummy buffer of 10 megabytes is allocated last, touched and then
> released to verify that there is a bit of spare memory left.
>
> This solution proved to work well on the embedded system. In some rare
> occasions with a larger amount of processes, the OOM killer could kill the
> wrong process despite the leads, but that happened seldom enough so I did not
> care about making a better solution.
>
> Until now that is. Without the OOM killer, the hack does not work at all, so I
> need some new method. One idea is to verify at each malloc call that there is
> enough memory left in the system in order to service it and if not, return
> NULL. If the system has swap, the system would be defined to be out of memory
> if any of the allocated memory has to be put to swap disk (the convolver is
> realtime and thus needs realtime access to memory).
>
> The problem is to implement the function (user space please) that returns how
> many more bytes one can safely allocate without forcing anything to a swap or
> running the system out of memory. Perhaps it is possible to use /proc/meminfo
> to implement this?

2.4.24-pre1 readds the OOM killer as a configurable option.

2.4.24-pre1 with CONFIG_OOM_KILLER=y will work for you.