perf annotate: Improve memory usage for symbol histogram

Hello,

This is another series of memory optimization in perf annotate.

v2 changes:
 * fix a bug when offset is bigger than 16 bits


When perf annotate (or perf report/top with TUI) processes samples, it
needs to save the sample period (overhead) at instruction level.  For
now, it allocates an array to do that for the whole symbol when it
hits any new symbol.  This comes with a lot of waste since samples can
be very few and instructions span to multiple bytes.

For example, when a sample hits symbol 'foo' that has size of 100 and
that's the only sample falls into the symbol.  Then it needs to
allocate a symbol histogram (sym_hist) and the its size would be

  16 (header) + 16 (sym_hist_entry) * 100 (symbol_size) = 1616

But actually it just needs 32 (header + sym_hist_entry) bytes.  Things
get worse if the symbol size is bigger (and it doesn't have many
samples in different places).  Also note that it needs a separate
histogram for each event.

Let's split the sym_hist_entry and have it in a hash table so that it
can allocate only necessary entries.

No functional change intended.

Thanks,
Namhyung


Namhyung Kim (4):
  perf annotate: Add a hashmap for symbol histogram
  perf annotate: Calculate instruction overhead using hashmap
  perf annotate: Remove sym_hist.addr[] array
  perf annotate: Add comments in the data structures

 tools/perf/ui/gtk/annotate.c |  14 ++++-
 tools/perf/util/annotate.c   | 116 ++++++++++++++++++++++-------------
 tools/perf/util/annotate.h   |  86 +++++++++++++++++++++++---
 3 files changed, 159 insertions(+), 57 deletions(-)

-- 
2.44.0.rc1.240.g4c46232300-goog