in memory LRU, try to meet the deficit in one go

src/fellow_cache.c

@@ -3171,9 +3171,11 @@ fellow_cache_lru_work(struct worker *wrk, struct fellow_cache_lru *lru)
 			fellow_cache_lru_seg_evict_locked(fcs,
 			    &alloc, lru);
 			AZ(pthread_mutex_unlock(&fco->mtx));
-			AZ(pthread_mutex_unlock(&lru->lru_mtx));
 			AN(buddy_return_ptr_extent(rets, &alloc));
 			fco = NULL;
+			if (rets->size < lru->fc->membuddy->deficit)
+				continue;
+			AZ(pthread_mutex_unlock(&lru->lru_mtx));
 			break;
 		}
 		if (fcs->state == FCO_INCORE) {