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

[Namhyung Kim <namhyung@kernel.org>]

Hi Ian,

On Fri, Feb 21, 2025 at 10:10:05PM -0800, Ian Rogers wrote:
> 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

It's still small and hard to verify.  I've run the following command
before and after the change but didn't see a difference.

  $ sudo time -f %Mk ./perf record -a true
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 1.757 MB perf.data (563 samples) ]
  74724k

According to man time(1), %M is for max RSS.

Thanks,
Namhyung

> 
> 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
>