mempool: introduce mempool_is_saturated

Introduce a helper mempool_is_saturated(), which tells if the mempool is
under-filled or not. We need it to figure out whether it should be
freed right into the mempool or could be cached with top level caches.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/636aed30be8c35d78f45e244998bc6209283cccc.1667384020.git.asml.silence@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/mempool.h

@@ -30,6 +30,11 @@ static inline bool mempool_initialized(mempool_t *pool)
 	return pool->elements != NULL;
 }
 
+static inline bool mempool_is_saturated(mempool_t *pool)
+{
+	return READ_ONCE(pool->curr_nr) >= pool->min_nr;
+}
+
 void mempool_exit(mempool_t *pool);
 int mempool_init_node(mempool_t *pool, int min_nr, mempool_alloc_t *alloc_fn,
 		      mempool_free_t *free_fn, void *pool_data,