[PATCH v3 0/8] Add io_dir to avoid memory overhead from opendir

[Ian Rogers <irogers@google.com>]

glibc's opendir allocates a minimum of 32kb, when called recursively
for a directory tree the memory consumption can add up - nearly 300kb
during perf start-up when processing modules. Add a stack allocated
variant of readdir sized a little more than 1kb

v3: Rebase on top of Krzysztof Łopatowski's work. Add additional
    defines for SYS_getdents64 on all other architectures if its
    definition is missing. Add a patch to further reduce the
    stack/memory usage in machine__set_modules_path_dir by appending
    to a buffer rather than creating a copy.
v2: Remove the feature test and always use a perf supplied getdents64
    to workaround an Alpine Linux issue in v1:
    https://lore.kernel.org/lkml/20231207050433.1426834-1-irogers@google.com/
    As suggested by Krzysztof Łopatowski
    <krzysztof.m.lopatowski@gmail.com> who also pointed to the perf
    trace performance improvements in start-up time eliminating stat
    calls can achieve:
    https://lore.kernel.org/lkml/20250206113314.335376-2-krzysztof.m.lopatowski@gmail.com/
    Convert parse-events and hwmon_pmu to use io_dir.
v1: This was previously part of the memory saving change set:
    https://lore.kernel.org/lkml/20231127220902.1315692-1-irogers@google.com/
    It is separated here and a feature check and syscall workaround
    for missing getdents64 added.

Ian Rogers (8):
  tools lib api: Add io_dir an allocation free readdir alternative
  perf maps: Switch modules tree walk to io_dir__readdir
  perf pmu: Switch to io_dir__readdir
  perf header: Switch mem topology to io_dir__readdir
  perf events: Remove scandir in thread synthesis
  perf parse-events: Switch tracepoints to io_dir__readdir
  perf hwmon_pmu: Switch event discovery to io_dir__readdir
  perf machine: Reuse module path buffer

 tools/lib/api/Makefile             |   2 +-
 tools/lib/api/io_dir.h             | 104 +++++++++++++++++++++++++++++
 tools/perf/util/header.c           |  31 ++++-----
 tools/perf/util/hwmon_pmu.c        |  42 +++++-------
 tools/perf/util/machine.c          |  57 ++++++++--------
 tools/perf/util/parse-events.c     |  32 +++++----
 tools/perf/util/pmu.c              |  46 ++++++-------
 tools/perf/util/pmus.c             |  30 +++------
 tools/perf/util/synthetic-events.c |  22 +++---
 9 files changed, 229 insertions(+), 137 deletions(-)
 create mode 100644 tools/lib/api/io_dir.h

-- 
2.48.1.658.g4767266eb4-goog