Re: [PATCH 2/3] jbd2: introduce jbd2_inode dirty range scoping

[Theodore Ts'o]

On Thu, Jun 20, 2019 at 09:09:11AM -0600, Ross Zwisler wrote:
> We could definitely keep separate dirty ranges for each of the current and
> next transaction.  I think the case where you would see a difference would be
> if you had multiple transactions in a row which grew the dirty range for a
> given jbd2_inode, and then had a random I/O workload which kept dirtying pages
> inside that enlarged dirty range.
> 
> I'm not sure how often this type of workload would be a problem.  For the
> workloads I've been testing which purely append to the inode, having a single
> dirty range per jbd2_inode is sufficient.

My inclination would be to keep things simple for now, unless we have
a real workload that tickles this.  In the long run I'm hoping to
remove the need to do writebacks from the journal thread altogether,
by always updating the metadata blocks *after* the I/O completes,
instead of before we submit the I/O.

					- Ted