Re: Page faults

[David Smith <dsmith at redhat dot com>]

On 09/10/2013 11:14 AM, Paddie O'Brien wrote:
> Thanks David. I tried your approach but I get the same result.
> 
> The script sometimes crashes unless I include --skip-badvars.
> 
> Could my problem be caused by a misconfigured systemtap installation?
> 
> Thanks,
> P

Hmm, interesting.  I tweaked the script a bit to use the 'target()'
function, which returns the pid of the target (from either '-c command'
or '-x pid').

====
global handled

probe kernel.function("filemap_fault")
{
        if (pid() != target()) next;
        printf("%s: filemap_fault\n", execname());
        printf("Page: %lu\n", $vmf->pgoff);
        handled[tid()] = 1
}
probe kernel.function("filemap_fault").return
{
        if (pid() != target()) next;
        delete handled[tid()]
}

probe kernel.function("find_get_page")
{
        if (handled[tid()] != 1) next;
        printf("%s: find_get_page\n", execname());
        printf("Page: %lu\n\n", $offset);
}
====

When I run "stap -c page_faults.stp -c ls", all the page numbers match up.

Since I didn't have to use '--skip-badvars', my next guess would be that
you've got an older systemtap.

I'm running HEAD systemtap (~2.3) on 3.11.0-0.rc5.git3.1.fc20.x86_64.
What version of systemtap and what kernel are you running?

-- 
David Smith
dsmith@redhat.com
Red Hat
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