nginx workers in "D" status in top

[Ryan Malayter]

I'm seeing a number of workers periodically entering the "D" status in
top (uninteruptible sleep). Normally, this means it is blocking on
disk IO. However, I am using nginx 0.7.62 (default package) on Ubunutu
9.10, and I believe asynchronous IO should be enabled.

We are using proxy_cache, so there is some reading from disk in our
configuration (not just reverse proxy).

Is it normal to have nginx workers block on the disk even on an
asynchronous IO-capable system?

How can I check if nginx is actually using async IO?

My configuration is large, but I will post fragments if necessary. I
am using 4 worker processes on a single-CPU system (recently upped to
10 because of this issue).

Thanks,

-- 
RPM