The cost of soft/minor faults

Here is a complete graph of the memory use and fault count for a run of ls -lia.

As you can see there are only soft/minor faults here – as one would expect (this was a machine with a lot of memory), as the C library provides the ls function and it will be loaded in memory (presumably the filesystem information was also in memory).

But there are a lot of soft faults – and these too have a cost, even if nothing like the cost of a hard fault. For a start each soft page fault almost certainly indicates a miss in the processor cache.

The paper linked here also gives a lot of information about Linux’s generation of soft/minor faults and their performance impact – it seems that the kernel is designed to deliver system wide flexibility at the expense of performance.

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