Re: [PATCH 0/2] NFS: limit use of ACCESS cache for negative responses

[Trond Myklebust <trondmy@hammerspace.com>]

On Fri, 2022-08-26 at 10:59 -0400, Benjamin Coddington wrote:
> On 16 May 2022, at 21:36, Trond Myklebust wrote:
> > So until you have a different solution that doesn't impact the
> > client's
> > ability to cache permissions, then the answer is going to be "no"
> > to
> > these patches.
> 
> Hi Trond,
> 
> We have some folks negatively impacted by this issue as well.  Are
> you
> willing to consider this via a mount option?
> 
> Ben
> 

I don't see how that answers my concern.

I'd rather see us set up an explicit trigger mechanism. It doesn't have
to be particularly sophisticated. I can imagine just having a global,
or more likely a per-container, cookie that has a control mechanism in
/sys/fs/nfs, and that can be used to order all the inodes to invalidate
their permissions caches when you believe there is a need to do so.

i.e. you cache the value of the global cookie in the inode, and if you
notice a change, then that's the signal that you need to invalidate the
permissions cache before updating the cached value of the cookie.

That way, you have a mechanism that serves all purposes: it can do an
immediate one-time only flush, or you can set up a userspace job that
issues a global flush once every so often, e.g. using a cron job.

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com