drm/asahi: gpu: Add a max object count garbage limit

This ensures the garbage Vec does not grow beyond what is reasonable,
and probably reduces jank by doing more smaller GCs instead of big ones.

Signed-off-by: Asahi Lina <lina@asahilina.net>

Author: hoshinolina

drivers/gpu/drm/asahi/gpu.rs

@@ -93,7 +93,11 @@ const HALT_ENTER_TIMEOUT: Duration = Duration::from_millis(100);
 /// Maximum amount of firmware-private memory garbage allowed before collection.
 /// Collection flushes the FW cache and is expensive, so this needs to be
 /// reasonably high.
-const MAX_FW_ALLOC_GARBAGE: usize = 16 * 1024 * 1024;
+const MAX_FW_ALLOC_GARBAGE_BYTES: usize = 16 * 1024 * 1024;
+/// Maximum count of firmware-private memory garbage objects allowed before collection.
+/// This works out to 16K of memory in the garbage list (8 bytes each), which keeps us
+/// within the safe range for kmalloc (on 16K page systems).
+const MAX_FW_ALLOC_GARBAGE_OBJECTS: usize = 2048;
 
 /// Global allocators used for kernel-half structures.
 pub(crate) struct KernelAllocators {
@@ -1171,7 +1175,11 @@ impl GpuManager for GpuManager::ver {
         let (garbage_count, garbage_bytes) = guard.private.garbage();
         let (ro_garbage_count, ro_garbage_bytes) = guard.gpu_ro.garbage();
 
-        if garbage_bytes > MAX_FW_ALLOC_GARBAGE || ro_garbage_bytes > MAX_FW_ALLOC_GARBAGE {
+        if garbage_bytes > MAX_FW_ALLOC_GARBAGE_BYTES
+            || ro_garbage_bytes > MAX_FW_ALLOC_GARBAGE_BYTES
+            || garbage_count > MAX_FW_ALLOC_GARBAGE_OBJECTS
+            || ro_garbage_count > MAX_FW_ALLOC_GARBAGE_OBJECTS
+        {
             mod_dev_dbg!(
                 self.dev,
                 "Collecting kalloc garbage (private: {} objects, {} bytes, gpuro: {} objects, {} bytes)\n",