bdflush or others affecting disk cache

["Jason Lim" <maillist@jasonlim.com>]

Hi all,

I've been banging my head on this one for a while now on a 2.4.20 system.
Here is the output of top:

Mem:  1027212K av, 1018600K used,    8612K free,       0K shrd,   70728K
buff
Swap: 2097136K av,   35556K used, 2061580K free                  690140K
cached


and the output of free:

             total       used       free     shared    buffers     cached
Mem:       1027212    1016256      10956          0      71528     683956
-/+ buffers/cache:     260772     766440
Swap:      2097136      34692    2062444


The problem is that swap usage can grow to 100Mb... yet the buffers and
cache remain at astoundingly high levels.

I can actually see memory to cache and buffers increasing and at the same
time see it increasing swap usage!

What I don't get is why the system... with about 700Mb in cache and 70Mb
in buffers, is using swap space at all.

I've searched high and low on Google... using phrases like "linux kernel
proc cache", buffers, bdflush, etc. but I still can't explain this.

Wouldn't it be far, FAR faster for the system to reduce the cache by about
100Mb or so instead of swapping that 100Mb to disk? And note that the swap
usage is constantly fluctuating, so you can see the performance problem
this is causing. Any ideas?!

Thanks in advance.

Jas