Closed karalabe closed 1 month ago
Here's a repro for the bug and the fix.
func BenchmarkHashTreeRootAllocBug(b *testing.B) {
obj := new(DepositData)
readValidGenericSSZ(nil, "../eth2.0-spec-tests/tests/mainnet/deneb/ssz_static/DepositData/ssz_random/case_4", obj)
b.ReportAllocs()
b.ResetTimer()
hh := ssz.NewHasherWithHashFn(gohashtree.HashByteSlice)
for i := 0; i < b.N; i++ {
obj.HashTreeRootWith(hh)
hh.Reset()
}
}
Without the PR:
go test ./spectests --run=NONE --bench=BenchmarkHashTreeRootAllocBug
BenchmarkHashTreeRootAllocBug-12 3209919 358.4 ns/op 192 B/op 1 allocs/op
With the PR:
go test ./spectests --run=NONE --bench=BenchmarkHashTreeRootAllocBug
BenchmarkHashTreeRootAllocBug-12 3425565 335.1 ns/op 0 B/op 0 allocs/op
This PR fixed a leaky allocation that happens in
merkleizeImpl
.Specifically, https://github.com/ferranbt/fastssz/blob/main/hasher.go#L379 expands the input slice:
but the problem is that the input slice is a sub-slice of h.buf, so if the expansion needs to allocate a new buffer because we're at capacity, then the newly allocated memory area gets thrown away and will not be piled into h.buf to be used subsequently. The result is that calls in a loop will allocate in a loop.
You can verify this by hashing
DepositData
for example, where the last field is 96 bytes, requiring a 32 byte expansion, but since it's at the end of the buffer, it will trigger the case.