Linux memory leak?

Donald Becker becker at scyld.com
Fri Mar 1 12:40:25 EST 2002


On Fri, 1 Mar 2002, Alan Scheinine wrote:

>   > Sometimes (e.g. after 14 days of
> normal operation) our nodes report unusually high memory usage even
> without any user processes active.
> 
>  Do you have a problem with paging to swap space?  My experience
> with Red Hat 6.2 is that memory fills up with everything I have
> used, such as files that have been read.  But that space is given
> to new processes when needed.  It seems that as much as possible is
> cached into memory.

There is a specific problem with the 2.4 kernels before 2.4.10, and
2.4.9 specifically.  The "lost" memory is _not_ being used as buffer
cache.  Instead it is unreferenced pages that the VM subsystem either
takes a long time to put on the free list, or are lost for all time.

This can be demonstrated by running a program that consumes a large
amount of data memory e.g. 1.5GB on a 2GB system used for intermediate
results.  When you run the same program a second time, there isn't
enough free memory and random processes are killed because of the memory
shortage.

Most Linux users don't notice this flaw because they run many smaller
programs that easily fit into the memory of a 2GB box.

Donald Becker				becker at scyld.com
Scyld Computing Corporation		http://www.scyld.com
410 Severn Ave. Suite 210		Second Generation Beowulf Clusters
Annapolis MD 21403			410-990-9993

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