On Wed, 2018-01-10 at 16:21 +0000, Harris, James R wrote:
> Hi Paul and Zhengyu,
> 
> The problem is that the app is not giving the block device a chance to
> complete any I/O while submitting the 520 back-to-back requests.  Blobstore is
> passive here – it does not do any polling on the block device – that is up to
> the application.

To additionally clarify - the bdev layer will poll for completions on your
behalf, but it does so on the same thread that you are submitting I/O from. If
you are in a tight loop submitting I/O and never yield back to the event
reactor, the polling won't have a chance to occur. You can either increase the
number of reqs per channel or submit smaller batches at a time. Basically, do
what Jim said below.

> Increasing the number of channel reqs would work – but at some point these
> will still run out.  So it really depends on your application – either
> increase the channel reqs to the absolutely maximum you will ever need, or add
> ENOMEM handling.