Re: [RFC 0/5] mm/bpf/perf: Store build id in file object

Namhyung Kim
2023-02-09T19:38:31Z

Hi Jiri,

On Thu, Feb 9, 2023 at 6:25 AM Jiri Olsa <olsajiri@gmail.com> wrote:
>
> On Wed, Feb 01, 2023 at 02:57:32PM +0100, Jiri Olsa wrote:
> > hi,
> > we have a use cases for bpf programs to use binary file's build id.
> >
> > After some attempts to add helpers/kfuncs [1] [2] Andrii had an idea [3]
> > to store build id directly in the file object. That would solve our use
> > case and might be beneficial for other profiling/tracing use cases with
> > bpf programs.
> >
> > This RFC patchset adds new config CONFIG_FILE_BUILD_ID option, which adds
> > build id object pointer to the file object when enabled. The build id is
> > read/populated when the file is mmap-ed.
> >
> > I also added bpf and perf changes that would benefit from this.

Thanks for working on this!

> >
> > I'm not sure what's the policy on adding stuff to file object, so apologies
> > if that's out of line. I'm open to any feedback or suggestions if there's
> > better place or way to do this.
>
> hi,
> Matthew suggested on irc to consider inode for storing build id

Yeah, that's my idea too.

>
> I tried that and it seems to have better stats wrt allocated build
> id objects, because inode is being shared among file objects
>
> I took /proc/slabinfo output after running bpf tests
>
> - build id stored in file:
>
> # name <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab> : tunables <limit> <batchcount> <sharedfactor> : slabdata <active_slabs> <num_slabs> <sharedavail>
> build_id 668 775 160 25 1 : tunables 0 0 0 : slabdata 31 31 0
>
> - build id stored in inode:
>
> # name <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab> : tunables <limit> <batchcount> <sharedfactor> : slabdata <active_slabs> <num_slabs> <sharedavail>
> build_id 222 225 160 25 1 : tunables 0 0 0 : slabdata 9 9 0

Cool!

>
>
> I'm stranger to inode/fs/mm code so I'll spend some time checking on
> what I possibly broke in there before I send it, but I'd appreciate
> any early feedback ;-)
>
> the code is in here:
> git://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
> inode_build_id
>
> I'll send another version with inode if there's no objection

I'll take a look.

Thanks,
Namhyung

> >
> > [1] https://lore.kernel.org/bpf/20221108222027.3409437-1-jolsa@kernel.org/
> > [2] https://lore.kernel.org/bpf/20221128132915.141211-1-jolsa@kernel.org/
> > [3] https://lore.kernel.org/bpf/CAEf4BzaZCUoxN_X2ALXwQeFTCwtL17R4P_B_-hUCcidfyO2xyQ@mail.gmail.com/
> > ---
> > Jiri Olsa (5):
> > mm: Store build id in file object
> > bpf: Use file object build id in stackmap
> > perf: Use file object build id in perf_event_mmap_event
> > selftests/bpf: Add file_build_id test
> > selftests/bpf: Add iter_task_vma_buildid test
> >
> > fs/file_table.c | 3 +++
> > include/linux/buildid.h | 17 +++++++++++++++++
> > include/linux/fs.h | 3 +++
> > kernel/bpf/stackmap.c | 8 ++++++++
> > kernel/events/core.c | 43 +++++++++++++++++++++++++++++++++++++++----
> > lib/buildid.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
> > mm/Kconfig | 7 +++++++
> > mm/mmap.c | 15 +++++++++++++++
> > tools/testing/selftests/bpf/prog_tests/bpf_iter.c | 88 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > tools/testing/selftests/bpf/prog_tests/file_build_id.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > tools/testing/selftests/bpf/progs/bpf_iter_task_vma_buildid.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
> > tools/testing/selftests/bpf/progs/file_build_id.c | 34 ++++++++++++++++++++++++++++++++++
> > tools/testing/selftests/bpf/trace_helpers.c | 35 +++++++++++++++++++++++++++++++++++
> > tools/testing/selftests/bpf/trace_helpers.h | 1 +
> > 14 files changed, 413 insertions(+), 4 deletions(-)
> > create mode 100644 tools/testing/selftests/bpf/prog_tests/file_build_id.c
> > create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_task_vma_buildid.c
> > create mode 100644 tools/testing/selftests/bpf/progs/file_build_id.c