@unclejack Could you describe how it helps save memory? Also #12899 definitely has origins in never-removed execConfig structs.

@LK4D4 execConfig structs are moste likely a small part of this. This saves memory by avoiding the allocation of io.Copy buffers. This saves about 96 KB per exec.

Makes sense to write own Copy function for this.

@LK4D4 Fair enough, I'll add it to pools.

@LK4D4 Sorry to disagree with you here, but we should avoid having a specialized version of io.Copy. It is a subtle function to get right. io.Copy can defer buffer allocation with ReaderFrom and WriterTo. Perhaps, a helper method like BufferedReaderFromSize(rd, size) would be appropriate.

@stevvooe but our function will be just wrapper around. Helper method not helping here, because we have hardcoded pools in pkg/pools.
So, we have four repetitions of same pattern, wrap reader to BufioReader from pool and use io.Copy, I think it make sense to wrap it to function.

@LK4D4 It's done. I've added it as a package level exported function for convenience.
@stevvooe As @LK4D4 said, it was only going to be a wrapper, not a full implementation of io.Copy.

@unclejack Looks like some tests are broken.

@LK4D4 I've reproduced the failure and I'm working on fixing it right away.

@LK4D4 The tests seem to be OK now. There's more work to be done for this, but this is good enough for one PR.

LGTM