I have moved from the CentOS 4.4 kernel to a 2.6.16.29 kernel.org kernel due to some vm problems I was having.

All has gone well except that my free memory now sits at 150MB. It does not like to go above or below that. Basically, 150MB of the system's memory is wasted. Andi Kleen suggested that I try tuning /proc/sys/vm/lowmem_reserve_ratio.

The problem is that lowmem_reserve_ratio appears to be undocumented.

Does anyone here happen to know how it works? The most I've been able to gather is that it sets the ratio of dirty to free pages for each of the memory zones.

The default on this server is: 256 256 32

Increasing the third number of seems to help, but I would really like to understand what it is that I am doing.

Thanks for any assistance, Steve Bergman