On Fri, Dec 14, 2018 at 8:08 PM Coly Li <colyli@xxxxxxx> wrote:
> Commit b1092c9af9ed ("bcache: allow quick writeback when backing idle")
> just looks at single bcache device. If there are I/Os for other bcache
> device on the cache set, and a single bcache device is idle, a faster
> writeback rate for this single idle bcache device will happen, I/O to
> read dirty data on cache for writeback will have negative impact to I/O
> requests of other bcache devices.
Yes, but this will potentially fill the queue on the idle device. If
you have an application that is intermittently doing I/O every few
seconds, the latency of the individual I/Os will be high. I was told
during review that this was unacceptable, and revised my patch. But
now we have merged a change that is more like my first patch that was
rejected...
Mike
