io_uring/alloc_cache: shrink default max entries from 512 to 128

In practice, we just need to recycle a few elements for (by far) most
use cases. Shrink the total size down from 512 to 128, which should be
more than plenty.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/alloc_cache.h

@@ -4,7 +4,7 @@
 /*
  * Don't allow the cache to grow beyond this size.
  */
-#define IO_ALLOC_CACHE_MAX	512
+#define IO_ALLOC_CACHE_MAX	128
 
 struct io_cache_entry {
 	struct io_wq_work_node node;