Re: Understand a semantic error in this simplistic kernel function counter script

[fche at redhat dot com (Frank Ch. Eigler)]

leonconstantin.fopa wrote:

> [...]
> I am writing a systemTap script to count the number of time the
> free_hot_page kernel function is call during every 5 seconds.

OK.

> probe timer.s(5) {
>       free_hot_page <<< 0

BTW, what is that <<< 0 intended to do?  It won't change the @sum.
In very old versions of systemtap, @sum() of an empty aggregate
caused an error, but it has evaluated to 0 since version 1.5
(2011-05-23).


> However, running this simple code produce semantic error (see below).
> What does this error means and how to fix the problem ?
> [...]
> semantic error: while resolving probe point: identifier 'kernel' at
> count-page-cache-release.stp:13:7
>         source : probe kernel.function("free_hot_page"){
>                       ^
>
> semantic error: no match (similar functions: free_arg_page,
> free_huge_page, free_one_page, free_p2m_page, __free_one_page)
>
> Pass 2: analysis failed.  [man error::pass2] 

It means that it could not find a function called free_hot_page in the
kernel, and is suggesting a few similarly-named functions that you may
have meant instead.  Maybe you meant "free_hot_cold_page" ?  Use
%  stap -l 'kernel.function("free*page*")'

See also 
% man error::pass2
which gives relevant advice.


- FChE