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I have been collecting the output of "free" command to keep an eye on the memory usage. I can see that there was a drastic change in the memory usage. See the ouput below it hsows the used memory drops from 11GB to 1.8GB. Why is that so?
After running that command I found there is a process taking highest memory of 711MB.
Still I have more Q - why does the size of used memory on the server get on increasing? If I sum up the memory used by all the processes in ps command, it doesn't equal to the used memory shown using free command.
Who is using the remaining memory? and why does it(total used memory) suddenly become very less?
We too have seen similar behaviour on RHEL4 systems. This seems to be down to the way linux uses available memory to speed up I/O by allocating it to cache. If you look, where you have a smaller amount of free RAM, you will notice the cache value has increased. This is normal behvaiour, and as RAM is needed to execute processes it is taken away from cache and realocated accordingly. Linux tries to make the best use it can of all available RAM. There was a big problem with this in RHEL3 Update 3 and below however where a kernel parameter /proc/sys/vm/pagecache) was set such that the system could potentially allocate 100% of RAM to cache, and thus start swapping out active processes which would eventually result in the system hanging, but I think the management of this is handled much better in RHEL4 with the 2.6 kernel.
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