TASK_CTX_STRIDE
nr_pages = (max_tasks * TASK_CTX_STRIDE + PAGE_SIZE - 1) / PAGE_SIZE;
task_ctx_t *cur = (task_ctx_t *)(slab + i * TASK_CTX_STRIDE);
(task_ctx_t *)(slab + (i + 1) * TASK_CTX_STRIDE) : NULL;