linux-kernel - Re: [PATCH 13/17] watch_queue: Implement mount topology and attribute change notifications [ver #5]

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Date:   Fri, 24 Jul 2020 18:44:01 +0800
From:   Ian Kent <raven@...maw.net>
To:     David Howells <dhowells@...hat.com>,
        Miklos Szeredi <miklos@...redi.hu>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Stephen Smalley <sds@...ho.nsa.gov>, nicolas.dichtel@...nd.com,
        Christian Brauner <christian@...uner.io>, andres@...razel.de,
        Jeff Layton <jlayton@...hat.com>, dray@...hat.com,
        Karel Zak <kzak@...hat.com>, keyrings@...r.kernel.org,
        Linux API <linux-api@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org,
        LSM <linux-security-module@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 13/17] watch_queue: Implement mount topology and
 attribute change notifications [ver #5]

On Fri, 2020-07-24 at 11:19 +0100, David Howells wrote:
> David Howells <dhowells@...hat.com> 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:-/

I was wondering about id re-use.

Assuming that ids that are returned to the idr db are re-used
what would the chance that a recently used id would end up
being used?

Would that chance increase as ids are consumed and freed over
time?

Yeah, it's one of those questions ... ;)

Ian