Messages in this thread | | | From | Roland McGrath <> | Subject | Re: [PATCH -mm v6] tracepoint: Add signal coredump tracepoint | Date | Tue, 20 Apr 2010 17:18:56 -0700 (PDT) |
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> Add signal coredump tracepoint which shows signal number, > mm->flags, core file size limitation, the result of > coredump, and core file name.
The "retval" encoding seems a bit arcane. I wonder if it might be better to just have separate tracepoints for successful and failed dump attempts. Note that whether or not the dump succeeded is already available in (task->signal->group_exit_code & 0x80) as seen at exit or death tracing events.
> This tracepoint requirement comes mainly from the viewpoint of > administrators. [...]
The purposes you mention seem to be served well enough by this tracepoint. But I recall having the impression that one of the original motivating interests for tracing core-dump details was to understand when a giant core dump was responsible for huge amounts of i/o and/or memory thrashing. (Once you notice that happening, you might adjust coredump_filter settings to reduce the problem.) Your new tracepoint doesn't help directly with tracking those sorts of issues, because it only happens after all the work is done. If you are monitoring trace_signal_deliver, then you can filter those for SIG_DFL cases of sig_kernel_coredump() signals and recognize that as the beginning of the coredump. Still, it might be preferable to have explicit start-core-dump and end-core-dump tracepoints.
Furthermore, I can see potential use for tracepoints before and after coredump_wait(), which synchronizes other threads before actually starting to calculate and write the dump. The window after coredump_wait() and before the post-dump tracepoint is where the actual work of writing the core file takes place, in case you want to monitor i/o load between those marks or suchlike.
> - char corename[CORENAME_MAX_SIZE + 1]; > + char corename[CORENAME_MAX_SIZE + 1] = "";
This initialization of a stack array means the same as:
memset(corename, '\0', sizeof corename);
So the compiler generates that because those are the semantics. All you need is:
corename[0] = '\0';
since this is a string.
Thanks, Roland
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