Question about memory usage

stefaandk · 08-02-2005, 07:09 PM

Mem: 1029168k av, 972696k used, 56472k free, 0k shrd, 238064k buff
703988k actv, 120k in_d, 20760k in_c
Swap: 1052248k av, 103600k used, 948648k free 471912k cached

looking at the above from the top command I see I have a gig of ram and 970MB of that in use while only 56 megs free.

However 470 megs of that is cached.

I'm confused about which part of this memory is actually used?

Is cached in use, if not why do I have only 56 megs free and isn't everything in cache?

Thx

marghorp · 08-02-2005, 07:15 PM

I read an answer to this question on this forum once. Can't find it now, but I believe Linux caches memory that's why most of it is used up most of the time. After a heavy load anyway. Why not all the memory? Probably something to do with the OS leaving empty memory for it's operations. I believe it is the buffer for cache in some strange words. Because swaping of pages from the cache takes time, the OS leaves some portion of the memory free at all times so new stuff can come in the memory without using swap all the time.

stefaandk · 08-02-2005, 07:25 PM

Thx,

I want to be able to find out whether my machine is running out of ram basically and
this "cache" makes it quite hard to come to a valid conclusion.

marghorp · 08-03-2005, 02:22 AM

The simplest way to see if your machine is running out of RAM is to see if SWAP is used. In normal conditions swap would never be used and only physical ram will be used. So if free -m command says that swap is anything but 100% free you are running out of RAM. But don't run free -m after heavy load, because heavy load eats up memory and swap will probably be used, but hey that's what swap is for.