Re: [PATCH v4 2/2] NFSD: add shrinker to reap courtesy clients on low memory condition

[bfields@fieldses.org (J. Bruce Fields)]

On Sat, Sep 03, 2022 at 10:59:17AM -0700, dai.ngo@oracle.com wrote:
> On 9/3/22 10:29 AM, Chuck Lever III wrote:
> >What I was suggesting was a longer term strategy for improving the
> >laundromat. In order to scale well in the number of clients, it
> >needs to schedule client expiry and deletion without serializing.
> >
> >(ie, the laundromat itself can identify a set of clients to clean,
> >but then it should pass that list to other workers so it can run
> >again as soon as it needs to -- and that also means it can use more
> >than just one CPU at a time to do its work).
> 
> I see. Currently on my lowly 1-CPU VM it takes about ~35 secs to
> destroy 128 clients, each with only few states (generated by pynfs's
> CID5 test). We can improve on this.

Careful--it's not the CPU that's the issue, it's waiting for disk.

If you're on a hard drive, for example, it's going to take at least one
seek (probably at least 10ms) to expire a single client, so you're never
going to destroy more than 100 per second.  That's what you need to
parallelize.  See item 3 from

	https://lore.kernel.org/linux-nfs/20220523154026.GD24163@fieldses.org/

Also, looks like current nfs-utils is still doing 3 commits per expiry.

Steve, for some reason I think "nfsdcld: use WAL journal for faster
commits" never got applied:

	https://lore.kernel.org/linux-nfs/20220104222445.GF12040@fieldses.org/

--b.