# Re: \[PATCH 13/17\] watch\_queue: Implement mount topology and attribute change notifications \[ver \#5\]

- From: David Howells \<dhowells@redhat.com\>
- Date: 2020-07-24 10:20:11 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2020/07/185090
- Thread: https://ratatoskr.run/keyrings/2020/03/175521/t.md

```text
David Howells [ref] wrote:

> > What guarantees that mount_id is going to remain a 32bit entity?
> 
> You think it likely we'd have >4 billion concurrent mounts on a system?  That
> would require >1.2TiB of RAM just for the struct mount allocations.
> 
> But I can expand it to __u64.

That said, sys_name_to_handle_at() assumes it's a 32-bit signed integer, so
we're currently limited to ~2 billion concurrent mounts:-/

David

```