While plotting vmstat data from various servers I saw a strange and very
regular pattern in the freememory status of just about any server. If there
was an odle period then the server would quickly recover memory pages not
used and then settle into this nifty pattern :
http://www.blastwave.org/dclarke/stuff/thor_free.png
If you were to see this over a longer period of time then you would see a
ever descending set of sharksteeth in the pattern. Very slowly over hours
the server eats up pages of memory. Not very much mind you but a definate
trend. Then .. after a period of time .. and avalance of recovery occurs
and the process begins again.
http://www.blastwave.org/dclarke/stuff/v655_free.png
or this :
http://www.blastwave.org/dclarke/stuff/thor_free2.png
Its quite fascinating to watch over a long period of time. If I can get a
long data set then I'll post it. Over a long period of time it looks like
memory will keep on being used forever and then whop! [1] all of it gets
recovered. Must be the free page scanner at work in the kernel ?
--
Dennis Clarke
[1] insert the sound of a hundred thousand people all saying "whop"
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