Re: [PATCH BUGFIX/IMPROVEMENT 0/4] block, bfq: series of fixes of bugs affecting service guarantees

From: Jens Axboe
Date: Tue Oct 03 2017 - 10:41:18 EST

On 09/21/2017 03:03 AM, Paolo Valente wrote:
> Hi,
> the first patch in this series fixes a bug that causes bfq to fail to
> guarantee a high responsiveness on some drives, if there is heavy
> random read+write I/O in the background. More precisely, such a
> failure allowed this bug to be found [1], but the bug may well cause
> other yet unreported anomalies.
> This fix uncovered other bugs that were concealed by the fixed bug,
> for rather subtle reasons. These further bugs caused similar
> responsiveness failures, but with sequential reaad+write workloads in
> the background. The remaining three patches fix these further bugs.
> The sum of these fixes makes responsiveness much stabler with BFQ. In
> the presence of write hogs, it is however still impossible for an I/O
> scheduler to guarantee perfect responsiveness in any circustance,
> because of throttling issues in the virtual-memory management
> subsystem, and in other higher-level components.

Added for 4.15, thanks.

Jens Axboe