chore(blooms): Reduce memory footprint of download queue (#18242)

The download queue has a fixed size of 100k elements and is implemented using a channel. Since the channel has a fixed size, this will allocate `capacity * object size`, where the object is `downloadRequest[BlockRef, BlockDirectory]`.

This PR changes the channel from a channel of objects (`chan downloadRequest[T, R]`) to a channel of pointers (`chan *downloadRequest[T, R]`) which should significantly reduce the permanently allocated memory for the queue.

Signed-off-by: Christian Haudum <christian.haudum@gmail.com>

pkg/storage/stores/shipper/bloomshipper/fetcher.go

@@ -484,7 +484,7 @@ type downloadResponse[R any] struct {
 }
 
 type downloadQueue[T any, R any] struct {
-	queue         chan downloadRequest[T, R]
+	queue         chan *downloadRequest[T, R]
 	enqueued      *swiss.Map[string, struct{}]
 	enqueuedMutex sync.Mutex
 	mu            keymutex.KeyMutex
@@ -502,7 +502,7 @@ func newDownloadQueue[T any, R any](size, workers int, process processFunc[T, R]
 		return nil, errors.New("queue requires at least 1 worker")
 	}
 	q := &downloadQueue[T, R]{
-		queue:    make(chan downloadRequest[T, R], size),
+		queue:    make(chan *downloadRequest[T, R], size),
 		enqueued: swiss.NewMap[string, struct{}](uint32(size)),
 		mu:       keymutex.NewHashed(workers),
 		done:     make(chan struct{}),
@@ -518,7 +518,7 @@ func newDownloadQueue[T any, R any](size, workers int, process processFunc[T, R]
 
 func (q *downloadQueue[T, R]) enqueue(t downloadRequest[T, R]) {
 	if !t.async {
-		q.queue <- t
+		q.queue <- &t
 		return
 	}
 	// for async task we attempt to dedupe task already in progress.
@@ -528,7 +528,7 @@ func (q *downloadQueue[T, R]) enqueue(t downloadRequest[T, R]) {
 		return
 	}
 	select {
-	case q.queue <- t:
+	case q.queue <- &t:
 		q.enqueued.Put(t.key, struct{}{})
 	default:
 		// todo we probably want a metric on dropped items
@@ -544,7 +544,7 @@ func (q *downloadQueue[T, R]) runWorker() {
 		case <-q.done:
 			return
 		case task := <-q.queue:
-			q.do(task.ctx, task)
+			q.do(task.ctx, *task)
 		}
 	}
 }