# 7.3. Controlling data transfer

Morloc Manual > Building APIs | https://morloc-project.github.io/docs/apis/data-transfer.html | prev: https://morloc-project.github.io/docs/apis/exposing-native-resources.md | next: https://morloc-project.github.io/docs/apis/api-interfaces.md

When a Morloc value crosses a pool boundary, the runtime picks one of three routes for data transfer:

-   **Inline** — for serialized payloads that are less than 64 KiB (by default), the bytes ride inside the packet over the Unix socket.
-   **Shared memory** — for larger payloads, the data sits in `/dev/shm` and the packet carries only an 8-byte pointer. This allows zero-copy data transfer between pools on the same host.
-   **Temp file** — only used when shared memory has been disabled (see `--no-shm` below). The data is written to a `.mpk` file and the packet carries the path.

Three `morloc make` flags let you override the default policy when it is wrong for your workload — restricted containers, tight `/dev/shm` quotas, debugging the wire-level traffic, or simply tuning the threshold to a value that matches your data shape:

| Flag | Effect |
| --- | --- |
| `--inline-size BYTES` | Move the inline/large threshold. Accepts a bare number or `k`/`m`/`g` suffix (binary, 1024-based). `0` means never inline. Default: `64k`. |
| `--no-shm` | Disable shared memory. Payloads above the inline threshold are written to a temp file and passed by path. |
| `--tmpdir PATH` | Directory for the temp files produced under `--no-shm`. **When set, the files are NOT auto-deleted at end of eval** — useful for testing and debugging. Default (unset): `$TMPDIR` or `/tmp`, with auto-cleanup at end of every eval. |

## 7.3.1. Combinations

| Build flags | Behavior |
| --- | --- |
| (none) | Inline `⇐ 64k`, shared memory above. |
| `--inline-size 0` | Never inline; all cross-pool transfers go through shared memory. |
| `--no-shm` | Inline `⇐ 64k`, temp files above. No `/dev/shm` traffic. |
| `--inline-size 0 --no-shm` | Every cross-pool transfer is a temp file. Slowest mode, but works on systems with no shared memory at all. |

## 7.3.2. Examples

Build for a container with no usable `/dev/shm`:

```console
$ morloc make --no-shm -o nexus main.loc
```

Run a workload where 64 KiB is too small (large records, every call exceeds the default):

```console
$ morloc make --inline-size 1m -o nexus main.loc
```

Inspect the wire-level packets for debugging or testing:

```console
$ morloc make --no-shm --inline-size 0 --tmpdir ./wire-dump -o nexus main.loc
$ ./nexus pipeline arg1 arg2
$ ls wire-dump/
morloc-pkt-12345-0.mpk  morloc-pkt-12345-1.mpk  ...
```

Each file is a self-contained MessagePack payload — one per pool return. Because `--tmpdir` was supplied, they persist after the program exits and can be inspected with any MessagePack reader.