Tuesday, 25 October 2011

dtrace update - attempting the vminfo probe

I've started tackling the vminfo probe provider, which is effectively
an SDT probe - statically compiled into the kernel. The approach is a
hands-off on the kernel source, but I have a tactic which I hope
will work.

Theres some issues, such as slightly different code for 32 vs 64 bit
kernel, but the approach seems sound.

In effect, this is a google map of the kernel binary - searching the
kernel for the instructions which represent increments to the
vmstat data counters, and enabling them for probes.

Will report back in a while if this looks good enough to use.
Many of the other providers are similar in style, but there are some
issues, such as not all counters in the kernel follow the vmstat
pattern. There is also the issue of provider function names
matching Solaris (some will, some will be extras). And also the callback
arguments need to match Solaris spec or something useful (more troublesome).

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