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

Jiri Olsa
2023-02-09T14:18:34Z

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.
>
> 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

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

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

thanks,
jirka

>
> thanks,
> jirka
>
>
> [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