Re: [PATCH v2 00/13] dso/dsos memory savings and clean up

[Namhyung Kim]

Hi Ian,

On Thu, Mar 21, 2024 at 9:03 AM Ian Rogers <irogers@xxxxxxxxxx> wrote:
>
> 13 more patches from:
> https://lore.kernel.org/lkml/20240202061532.1939474-1-irogers@xxxxxxxxxx/
> a near half year old adventure in trying to lower perf's dynamic
> memory use. Bits like the memory overhead of opendir are on the
> sidelines for now, too much fighting over how
> distributions/C-libraries present getdents. These changes are more
> good old fashioned replace an rb-tree with a sorted array and add
> reference count tracking.
>
> The changes migrate dsos code, the collection of dso structs, more
> into the dsos.c/dsos.h files. As with maps and threads, this is done
> so the internals can be changed - replacing a linked list (for fast
> iteration) and an rb-tree (for fast finds) with a lazily sorted
> array. The complexity of operations remain roughly the same, although
> iterating an array is likely faster than iterating a linked list, the
> memory usage is at least reduce by half.
>
> As fixing the memory usage necessitates changing operations like find,
> modify these operations so that they increment the reference count to
> avoid races like a find in dsos and a remove. Similarly tighten up
> lock usage so that operations working on dsos state hold the
> appropriate lock.
>
> Here are some questions (with answers) that I am expecting from reviewers:
>
>  - Why not refactor dso with accessors first and then do the other things?
>
> My ambition with this change was to lower memory overhead not to
> particularly clean up and fix dso. Fixing the memory overhead, by
> refactoring and changing the internals, showed that locking discipline
> and reference counting discipline was lacking. The later changes try
> to fix these as a service to the community while I am changing the
> code and to also ensure that code is correct (more correct than it was
> wrt locking and reference counting than before the patches).
>
> Reordering the patches to do the refactoring first will be a giant
> pain. It will merge conflict with every other patch in the series and
> is basically a request to reimplement everything from square 1. The
> only thing I'd have in my favor would be how the code should look at
> the end of the series, and reordering patches doesn't change the
> eventual outcome of applying the patches. Note also, were I to send
> the memory saving patches and then a week later send the API clean up
> and reference counting fix patches the patches would be merged in the
> order they are here. I've done my best, I know you may consider that
> I'm adding to your reviewing overhead but I've also got to think about
> the overhead to me.
>
>  - Please break apart this change...
>
> The first changes are moving things, but when a broken API is spotted
> like the missing get on dsos__find I put it in a change to move the
> function and to add the missed get. Could this be two changes? Yes, it
> could. Does moving code materially change the behavior of the tool?
> No. I've done it in one patch to minimize churn and to some extent for
> my sanity. Such changes are less than 100 lines of code and all
> independently tested.
>
>  - The logic in dso around short, long name and id with sorting is weird
>
> Yes, I've tried to make it less weird while retaining the existing
> behavior. It would be easy to make a series of patches just cleaning
> it up but I came here to save memory not change the dso API.
>
>  - Move the fixes in the 12th patch earlier.
>
> This is possible but then impossible to test with reference count
> checking. This does mean there are broken reference counts before the
> patch is applied, but this is generally already the case. Yes, some
> hypothetical person may decide to fork midway through this patch
> series and my order would mean they wouldn't have a fix. I've done my
> best while working within the bounds of my time and trying to avoid
> churn.
>
> v2. Rebases on top of tmp.perf-tools-next resolving merge conflicts.
>
> Ian Rogers (13):
>   perf dso: Reorder variables to save space in struct dso
>   perf dsos: Attempt to better abstract dsos internals
>   perf dsos: Tidy reference counting and locking
>   perf dsos: Add dsos__for_each_dso
>   perf dso: Move dso functions out of dsos
>   perf dsos: Switch more loops to dsos__for_each_dso
>   perf dsos: Switch backing storage to array from rbtree/list
>   perf dsos: Remove __dsos__addnew
>   perf dsos: Remove __dsos__findnew_link_by_longname_id
>   perf dsos: Switch hand code to bsearch
>   perf dso: Add reference count checking and accessor functions
>   perf dso: Reference counting related fixes
>   perf dso: Use container_of to avoid a pointer in dso_data

Acked-by: Namhyung Kim <namhyung@xxxxxxxxxx>

Thanks,
Namhyung

>
>  tools/perf/builtin-annotate.c                 |   8 +-
>  tools/perf/builtin-buildid-cache.c            |   2 +-
>  tools/perf/builtin-buildid-list.c             |  18 +-
>  tools/perf/builtin-inject.c                   |  96 +--
>  tools/perf/builtin-kallsyms.c                 |   2 +-
>  tools/perf/builtin-mem.c                      |   4 +-
>  tools/perf/builtin-record.c                   |   2 +-
>  tools/perf/builtin-report.c                   |   6 +-
>  tools/perf/builtin-script.c                   |   8 +-
>  tools/perf/builtin-top.c                      |   4 +-
>  tools/perf/builtin-trace.c                    |   2 +-
>  tools/perf/tests/code-reading.c               |   8 +-
>  tools/perf/tests/dso-data.c                   |  67 ++-
>  tools/perf/tests/hists_common.c               |   6 +-
>  tools/perf/tests/hists_cumulate.c             |   4 +-
>  tools/perf/tests/hists_output.c               |   2 +-
>  tools/perf/tests/maps.c                       |   4 +-
>  tools/perf/tests/symbols.c                    |   8 +-
>  tools/perf/tests/vmlinux-kallsyms.c           |   6 +-
>  tools/perf/ui/browsers/annotate.c             |   6 +-
>  tools/perf/ui/browsers/hists.c                |   8 +-
>  tools/perf/ui/browsers/map.c                  |   4 +-
>  tools/perf/util/annotate-data.c               |  14 +-
>  tools/perf/util/annotate.c                    |  47 +-
>  tools/perf/util/auxtrace.c                    |   2 +-
>  tools/perf/util/block-info.c                  |   2 +-
>  tools/perf/util/bpf-event.c                   |   8 +-
>  tools/perf/util/build-id.c                    | 136 ++---
>  tools/perf/util/build-id.h                    |   2 -
>  tools/perf/util/callchain.c                   |   2 +-
>  tools/perf/util/data-convert-json.c           |   2 +-
>  tools/perf/util/db-export.c                   |   6 +-
>  tools/perf/util/dlfilter.c                    |  12 +-
>  tools/perf/util/dso.c                         | 472 +++++++++------
>  tools/perf/util/dso.h                         | 554 +++++++++++++++---
>  tools/perf/util/dsos.c                        | 529 +++++++++++------
>  tools/perf/util/dsos.h                        |  40 +-
>  tools/perf/util/event.c                       |   8 +-
>  tools/perf/util/header.c                      |   8 +-
>  tools/perf/util/hist.c                        |   4 +-
>  tools/perf/util/intel-pt.c                    |  22 +-
>  tools/perf/util/machine.c                     | 192 ++----
>  tools/perf/util/machine.h                     |   2 +
>  tools/perf/util/map.c                         |  82 ++-
>  tools/perf/util/maps.c                        |  14 +-
>  tools/perf/util/probe-event.c                 |  25 +-
>  .../util/scripting-engines/trace-event-perl.c |   6 +-
>  .../scripting-engines/trace-event-python.c    |  21 +-
>  tools/perf/util/session.c                     |  21 +
>  tools/perf/util/session.h                     |   2 +
>  tools/perf/util/sort.c                        |  19 +-
>  tools/perf/util/srcline.c                     |  65 +-
>  tools/perf/util/symbol-elf.c                  | 145 +++--
>  tools/perf/util/symbol-minimal.c              |   4 +-
>  tools/perf/util/symbol.c                      | 186 +++---
>  tools/perf/util/symbol_fprintf.c              |   4 +-
>  tools/perf/util/synthetic-events.c            |  24 +-
>  tools/perf/util/thread.c                      |   4 +-
>  tools/perf/util/unwind-libunwind-local.c      |  18 +-
>  tools/perf/util/unwind-libunwind.c            |   2 +-
>  tools/perf/util/vdso.c                        |  56 +-
>  61 files changed, 1817 insertions(+), 1220 deletions(-)
>
> --
> 2.44.0.396.g6e790dbe36-goog
>