Re: Non-blocking socket stuck for multiple seconds on xfs_reclaim_inodes_ag()

[Kenton Varda <kenton@cloudflare.com>]

On Tue, Dec 25, 2018 at 3:47 PM Dave Chinner <david@fromorbit.com> wrote:
> But taking out your frustrations on the people who are trying to fix
> the problems you are seeing isn't productive. We are only a small
> team and we can't fix every problem that everyone reports
> immediately. Some things take time to fix.

I agree. My hope is that explaining our use case helps you make XFS
better, but you don't owe us anything. It's our problem to solve and
any help you give us is a favor.

> IOWs, there are relatively few applications that have such a
> significant dependency on memory reclaim having extremely low
> latency,

Hmm, I'm confused by this. Isn't low-latency memory allocation is a
common requirement for any kind of interactive workload? I don't see
what's unique about our use case in this respect. Any desktop and most
web servers I would think have similar requirements.

I'm sure there's something about our use case that's unusual, but it
doesn't seem to me that requiring low-latency memory allocation is
unique.

Maybe the real thing that's odd about us is that we constantly create
and delete files at a high rate, and that means we have an excessive
number of dirty inodes to flush?

> IOWs, we're trying to solve *all* the blocking problems that we know
> that can occur in inode reclaim so that it all just works for
> everyone without tweaks being necessary. Yes, this takes longer than
> just addressing the specific symptom that is causing you problems,
> but the reality is while fixing things properly takes time to get
> right, everyone will benefit from it being fixed and not just one or
> two very specific, latency sensitive workloads.

Great, it's good to hear that this problem is expected to be fixed
eventually. We can patch our way around it in the meantime.

-Kenton