ByteStream upload reads the whole blob into memory before sending #1565

upload_impl in remote_execution/oss/re_grpc/src/client.rs reads a blob into a Vec<WriteRequest> of all segments and only then calls ByteStream.Write with futures::stream::iter(segments). The memory used by one upload is the size of the blob. A 2 GiB file uploaded with --upload-all-actions or as a cache upload costs 2 GiB of heap.

The segments can be produced lazily and passed to write as a stream, so only the segment in flight and one read ahead are in memory.

https://github.com/facebook/buck2/blob/8c4e27d602/remote_execution/oss/re_grpc/src/client.rs#L1645-L1683