Tracking vm activity

[William Cohen]

Hi,

I am playing around with getting information about page faults and I noticed 
that there is a probe alias for the entry for the pagefault code. However, there 
is no matching probe point for the return. It is useful to look at the return 
value to determine what kind of page fault occurred (major or minor). The 
attached patch provides a similar probe point for the return point. any comments 
on the patch?

This would be useful for the following senario. A probe on vm.pagefault could 
get the address and a probe on vm.pagefault.return could get information how it 
was handled. The analysis could then do things like which addresses cause major 
page faults (real disk accesses). One could write out a log of the major page 
faults (and the mmap operations) and track which files caused the page faults. 
Probably don't want to walk through the mm structures when taking a page fault 
to determine which file it came from.

-Will
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