Please explain the following line from the "top" command in the bold :
Mem: 1026228k total, 449640k used, 576588k free, 44812k buffers
Swap: 1052248k total, 2020k used, 1050228k free, 189092k cached
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The “buffers” entry indicates how much of the memory in use is currently being used for disk buffering.
So long as these pages are not modified after they have been written to the swap file then the next time the page is swapped out there is no need to write it to the swap file as the page is already in the swap file. Instead the page can simply be discarded. In a heavily swapping system this saves many unnecessary and costly disk operations.
Linux automatically caches files read from the disk. That cache is called buffers. The buffers will be released, if your program wants more memory and no more is free.
I don't know what the cached swap means.
EDIT: I googled shortly for the swap and saw the following: http://www.linux-tutorial.info/modules.php?name=MContent&pageid=314
Seems that the cached swap means all the pages in the swap, that are reloaded into memory but unchanged since. These pages in the swap are already valid and if the page is swapped out later again Linux doesn't need to write them actually to the disk.