fedora 9 is caching too much memory

[abhayrathod]

Hi

I am having fedora 9 installed with RAM of 2 gigs. I have Vmserver installed on it and am running 1 Vm with 512 RAM allocated to it.

After powering ON the VM, total memory cached by fedora is 1283 Megs and free memory left is too less ~49 megs
---------------------------
# free -m
total used free shared buffers cached
Mem: 1981 1932 49 0 47 1283
-/+ buffers/cache: 601 1380
Swap: 1983 0 1983

---------------

Can any one please tell why fedora is caching so much of mem and how can we reduce it .

Thanks

[markkuk]

Unused memory is wasted memory. There's no problem with your memory use. If you start more programs that use more memory space, the amount used for caching will be reduced automatically.

[nt4cats]

Here is another way to look at it.

Consider the output from my machine:

[ddenardo@cylon ~]$ free -m
             total       used       free     shared    buffers     cached
Mem:          3964       3261        702          0         48       2158
-/+ buffers/cache:       1054       2909
Swap:         5951          0       5951

One line at a time (plus the header):

             total       used       free     shared    buffers     cached
Mem:          3964       3261        702          0         48       2158

I have 3964 megs of total RAM (~ 4Gigs), 3261M is "used", leaving 702M "free". The "shared" memory column is obsolete -- ignore it. The last two numbers say that I have 48M of kernel buffers, and 2158M of "Cached" stuff.

This looks like my RAM is more than 80% "full" (only 700M out of 4G of RAM is "free"). This isn't really true, and the next line explains that.

             total       used       free     shared    buffers     cached
-/+ buffers/cache:       1054       2909

That says that if you factor out the buffers and cache, I really have 1054M "used" and 2909M "free" -- so I'm really only using about 25% of my RAM at this point.

The last line (the one that starts with "Swap:") just shows the total amount of swap space available and the amount of swap space used.

... so you may wonder why the first line said that 80% of my RAM was being used? Well, the kernel realizes that I have gobs and gobs of unused RAM, so it does things like buffer disk reads -- which makes the computer faster. If an application needs that RAM that it is using for buffers, the kernel will discard the buffer and give the application the memory it asked for.

In your case, it looks like you only have 49M available, but in reality you have 1380M available.

Does that make sense?

[abhayrathod]

Thanks for that detailed explanation.

That explains my doubt about cache memory.

[sideways]

you can (temporarily) empty the cache with (as root)

sync && echo 3 > /proc/sys/vm/drop_caches

But there is no point, as it will be automatically freed if required for a process, and it will quickly fill up again anyway.

http://linux-mm.org/Drop_Caches