On Wed, Dec 11, 2024, at 9:46 AM, William Cohen wrote:
> Hi Serhei,
>
> The dwfl_report_proc_map() will handle when things are added to the
> memory map. Is there anything to handle the inverse event when memory
> is removed from the process memory map, such as a dlcose()?
>
Interestingly, linux/perf/tools/design.txt mentions an 'munmap' field in struct
perf_event_attr, but it doesn't seem to have made it into the actual kernel
implementation of perf_events. I'll have to do some more digging to find out
what happened with that idea between design and implementation.
If we have reason to believe that the process mappings are changing too
drastically to get sensible results with incremental updates,
sysprof-live-unwinder's current quick solution (i.e. re-scan the proc mappings
from scratch) is a feasible fallback. We just need a threshold for doing that
which is 'sensible, but not too frequent'. Even a time threshold might be worth
experimenting with for this. The main high-overhead case we're trying to avoid
is when a process loads then does mmap, mmap, mmap, and the profiler is
following this process from the start and reloading the Dwfl each time.
-- Serhei
