understanding memory usage
Hi,
I'm using 'free' to see memory usage on my ubuntu server 8.10. Can you please explain the difference between Mem and buffers/cache? I expect low memory usage but there is almost no free Mem. On the other hand there is a lot of free buffers/cache. total used free shared Mem: 1747764 1601008 146756 0 -/+ buffers/cache: 91864 1655900 Swap: 917496 496 917000 Thanks |
The line
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-/+ buffers/cache: 91864 1655900 |
what does it means that 1655900 is used by buffer/cache?
is it normal? Will ubuntu automatically decrease the cache if another application needs the memory? Can you please explain what are VIRT, RES and SHR when running 'top'? Thanks |
Roughly (because I've never found anything that explains these statistics precisely):
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RES is the amount of the process's memory currently physically mapped to actual ram. It might be misleadingly low because I think it excludes pages that could be soft faulted. In obscure cases it could be misleadingly high because pages might be double mapped (I think they would be double counted). In more common cases it will be misleadingly high because of shared (with other processes) mappings. But it is a fairly good measure of the physical ram footprint of a process. SHR is the amount of a process's virtual memory that is mapped in a way that it could be shared, for example the parts into which unmodified sections of .so files are loaded. But nothing tells you how much of that is actually shared nor how much of it is actually in physical memory. |
thanks.
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