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I have an application which periodically (after each 1 or 2 seconds) takes checkpoints by forking itself. So checkpoint is a fork of the original process which just stays idle until it is asked to start when some error in the original process occurs. Now my question is how costly is the copy-on-write mechanism of fork. How much is the cost of a page fault trap that will occur whenever the original process writes to a memory page (first time after taking a checkpoint that is), as copy-on-write mechanism will make sure that it gives the original process a different physical page than the checkpoint. In my opinion, the page fault trap overhead could be quite high as an interrupt occurs, we land from user-space land to the kernel space land and then back from kernel to user-space. How many CPU cycles can I lose from such a a page fault trap. Assume that the RAM is big enough and we don't ever need to swap to the hard disk. Well I know that its difficult to imagine a checkpointing scheme more efficient than this and therefore you could say why I'm worrying about page trap fault overhead, but I'm asking just to have an idea how much cost will be there for this scheme.

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