Cache memory never gets released

Here is /proc/meminfo from a box that has all but exhausted its free memory:
total: used: free: shared: buffers: cached:

Mem:  122064896 84348928 37715968        0   634880 74829824
Swap:        0        0        0
MemTotal:       119204 kB
MemFree:         36832 kB
MemShared:           0 kB
Buffers:           620 kB
Cached:          73076 kB
SwapCached:          0 kB
Active:          70380 kB
Inactive:         7324 kB
HighTotal:           0 kB
HighFree:            0 kB
LowTotal:       119204 kB
LowFree:         36832 kB
SwapTotal:           0 kB
SwapFree:            0 kB

Might as well suggest walking on water. The hardware is set in stone, this is a software issue :^).

Something is preventing the cached memory to get reused, it's like it's gone for good.

Is there any count of how often a cached block is accessed? If there is such a count, and the count has an effect on whether to allow the release of the cached block, that could explain this behaviour. Because it could turn out that the cached blocks are accessed thousands of times.

Thanks--
Dave

Are you sure you have a problem? If you do ls -R / on a file-system and then look at the cached RAM, you see a lot. It's the dircache. It is some of the first to be used when the system needs RAM. If you compile the kernel with make -j 20 bzImage so you have a lot of tasks, needing lots of RAM, the cached value goes way down. It will eventually be "free" after the compile completes.

Basically, the only way to return cached RAM to the free-list is to run programs requiring RAM. What is listed as "cached" really means "RAM that was used, but wasn't freed because we don't need it yet.... Freeing RAM is as expensive as acquiring it so if it's used by a kernel buffer, it isn't freed until it's needed.

This is linux-2.4.26. If you are using an exprimental kernel, memory-allocation might be broken but is probably not.

Cheers,
Dick Johnson
Penguin : Linux version 2.4.26 on an i686 machine (5570.56 BogoMips).
Note 96.31% of all statistics are fiction.