Adding new env variables for TPU backends. (huggingface#1755)

# What does this PR do?


On TPU (and probably inferentia). The model needs to know right off the
bat about BATCH_SIZE and MAX_TOTAL_TOKENS (since the entire cache will
be determined by both).

This PR sends that information to the shards to they can allocate
accordingly. Should be no-op for other backends.
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Fixes # (issue)


## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the
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      Pull Request section?
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launcher/src/main.rs

@@ -448,6 +448,8 @@ fn shard_manager(
     cuda_memory_fraction: f32,
     rope_scaling: Option<RopeScaling>,
     rope_factor: Option<f32>,
+    max_total_tokens: usize,
+    max_batch_size: Option<usize>,
     otlp_endpoint: Option<String>,
     status_sender: mpsc::Sender<ShardStatus>,
     shutdown: Arc<AtomicBool>,
@@ -512,6 +514,7 @@ fn shard_manager(
         (Some(scaling), Some(factor)) => Some((scaling, factor)),
         (None, Some(factor)) => Some((RopeScaling::Linear, factor)),
     };
+
     // OpenTelemetry
     if let Some(otlp_endpoint) = otlp_endpoint {
         shard_args.push("--otlp-endpoint".to_string());
@@ -564,6 +567,14 @@ fn shard_manager(
         envs.push(("ROPE_FACTOR".into(), factor.to_string().into()));
     }
 
+    envs.push((
+        "MAX_TOTAL_TOKENS".into(),
+        max_total_tokens.to_string().into(),
+    ));
+    if let Some(max_batch_size) = max_batch_size {
+        envs.push(("MAX_BATCH_SIZE".into(), max_batch_size.to_string().into()));
+    }
+
     // If huggingface_hub_cache is some, pass it to the shard
     // Useful when running inside a docker container
     if let Some(huggingface_hub_cache) = huggingface_hub_cache {
@@ -967,6 +978,7 @@ fn spawn_shards(
     num_shard: usize,
     args: &Args,
     cuda_graphs: Vec<usize>,
+    max_total_tokens: usize,
     shutdown: Arc<AtomicBool>,
     shutdown_receiver: &mpsc::Receiver<()>,
     shutdown_sender: mpsc::Sender<()>,
@@ -998,6 +1010,7 @@ fn spawn_shards(
         let cuda_memory_fraction = args.cuda_memory_fraction;
         let rope_scaling = args.rope_scaling;
         let rope_factor = args.rope_factor;
+        let max_batch_size = args.max_batch_size;
         thread::spawn(move || {
             shard_manager(
                 model_id,
@@ -1020,6 +1033,8 @@ fn spawn_shards(
                 cuda_memory_fraction,
                 rope_scaling,
                 rope_factor,
+                max_total_tokens,
+                max_batch_size,
                 otlp_endpoint,
                 status_sender,
                 shutdown,
@@ -1474,6 +1489,7 @@ fn main() -> Result<(), LauncherError> {
         num_shard,
         &args,
         cuda_graphs,
+        max_total_tokens,
         shutdown.clone(),
         &shutdown_receiver,
         shutdown_sender,