Reduce memory footprint when loading BTF

[zkonge]

Origin

I'm writing a very simple tracepoint eBPF program, which does not need BTF.
But I notice that while the program is running, the memory usage is far more large than I expected

Investigation

After running the memory profile, I found the program contains lots of fragmental allocations.
and it doesn't return memory to OS

Memory exactly used:

Memory allocation in full lifetime:

Here, the Btf::from_sys_fs() is even called twice.

EbpfLoader doesn't give any chance to prevent BTF loading, it load BTF at the struct initialization.

aya/aya/src/bpf.rs

Line 157 in ade2e2a

btf: Btf::from_sys_fs().ok().map(Cow::Owned),

and Ebpf::loadcauses the BTF double loading

aya/aya/src/bpf.rs

Lines 879 to 883 in ade2e2a

	pub fn load_file<P: AsRef<Path>>(path: P) -> Result<Self, EbpfError> {
	EbpfLoader::new()
	.btf(Btf::from_sys_fs().ok().as_ref())
	.load_file(path)
	}

Fixing

After I remove the Btf::from_sys_fs() in the EbpfLoader, the memory usage after calling Ebpf::load reduce to half.

Once I manually build Ebpf from EbpfLoader, the heap allocation is reduced to 150 KiB

More

Although not my use case, there is still a lot of room for optimization in BTF loading, such as arena (like bumpalo?) and using stack allocation instead of Vec abusing.

[dave-tucker]

Per the comment on the PR, the fix for your case is: https://docs.aya-rs.dev/aya/struct.ebpfloader#method.btf
Passing None here will disable BTF, but this may not be exactly what you want.

Although not my use case, there is still a lot of room for optimization in BTF loading, such as arena (like bumpalo?) and using stack allocation instead of Vec abusing.

I think it's worth leaving this issue open just for ☝