# Where the resident model's 7.9GB of RSS goes (2026-08-03, homesrv)

Measured for Vikunja #499. The deployed llama-server held 7.9GB RSS for a 1.1GB
model file. Half a gigabyte of it was in swap, on a box that also runs
whisper.cpp, piper and the embedder.

## Method

`maven-mavend-1` was stopped for the measurement, with the owner's approval.
Its own binary then ran on the host with the exact deployed command line. That
binary is `/opt/maven/bin/llama-server`, version `1 (4c65955)`, a Vulkan build.

```sh
llama-server -m /mnt/hdd1/llms/qwen3/Qwen3-1.7B-UD-Q4_K_XL.gguf \
  --host 127.0.0.1 --port 18099 -c 4096 -ngl 99 --no-webui
```

RSS was read from `/proc/<pid>/status` after load and after each of 8 distinct
1521-token prompts. `smaps` of the deployed process was read first, from inside
the container, since the host user cannot read another user's maps.

## The cause: the prompt cache, not the weights and not the offload

The startup log says it outright:

```text
srv load_model: prompt cache is enabled, size limit: 8192 MiB
srv llama_server: n_parallel is set to auto, using n_parallel = 4 and kv_unified = true
```

The server saves the full KV state of every idle slot it evicts. It keeps up to
8GiB of those states in host RAM (llama.cpp PR 16391). One saved prompt of 1521
tokens costs 166.377 MiB. That is 112 kiB per token, exactly Qwen3-1.7B's KV
footprint (28 layers x 2 x 1024 dims x 2 bytes).

RSS at rest, and per distinct prompt:

| Prompts served | RSS, default | RSS, `--cache-ram 512` |
|---|---|---|
| 0 (just loaded) | 443 MB | 411 MB |
| 1 | 445 MB | 411 MB |
| 4 | 958 MB | 929 MB |
| 8 | 1641 MB | 932 MB |

Uncapped, RSS climbs about 170MB per distinct prompt and does not stop until
the 8GiB limit. Capped at 512 MiB it plateaus at 932MB from the fourth prompt
on, with the cache holding steady at `3 prompts, 499.132 MiB` and evicting.

The 7.9GB on the running daemon was that climb, weeks of it. Its `smaps` showed
one 6.03GB anonymous mapping at 5.32GB resident plus a 1.45GB mapping at 1.27GB
resident, and only 30MB of file-backed RSS.

## The task's leading guess was wrong

`-ngl 99` on the Vega iGPU costs almost no process RSS. A freshly loaded server
has 95MB of anonymous RSS in total. RADV allocates device memory through the
kernel, outside the process, and the log sees 8202 MiB free on `Vulkan0`. The
weights are mmapped and file-backed, so they are evictable and do not pin RSS. The logit buffer is not visible in the numbers above at all.

## Decision

`--cache-ram 512` is now the default, wired as `phraser.cache_ram_mib` and set
in `deploy/mavend.json`. 512 MiB caps total RSS near 1GB, an eighth of what the
box carried. It still holds three of the 1521-token probes above. Maven's real
routing and phrasing prompts are much shorter, so it holds more of those than
the table suggests. `-c 4096` is untouched, as #499
required. A negative `cache_ram_mib` passes no flag, for a llama-server too old
to know it.

Not changed: `n_parallel = 4`. With `kv_unified = true` the four slots share one
4096-token KV cache, so they do not multiply it.

The other half of #499 was that none of these lines were reachable. mavend
scraped llama-server's stderr for the listen line and discarded it, and never
piped stdout at all. Both streams now go to mavend's log with a `llama:` prefix.
The last 12 startup lines go into the error when the server dies before it
listens.

## Deployed

The `mavenai:latest` image was rebuilt and `maven-mavend-1` recreated the same
day. The daemon's own log now carries the child's startup, it reads
`prompt cache is enabled, size limit: 512 MiB`, and the resident server sat at
439MB RSS after load and 613MB after one served turn.
