Re: Loosing transactions

[Kent Overstreet <koverstreet-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>]

On Mon, Jan 28, 2013 at 03:45:23PM +0100, Pierre Beck wrote:
> 
> >We probably want to start by simplifying/narrowing it down a bit - we
> >can eliminate the possibility of the disk having anything to do with it
> >and just use the SSD by forcing everything to writeback mode:
> >
> >For that you'll want to disable both sequential bypass (echo 0 >
> >/sys/block/bcache/bcacheN/sequential_cutoff) and the congested
> >thresholds -
> >echo 0 > /sys/fs/bcache/<cache set>/congested_read_threshold_us,
> >echo 0 > /sys/fs/bcache/<cache set>/congested_write_threshold_us
> >
> >After that (assuming you're also in writeback mode) all writes will be
> >writeback writes until the device is more than half full of dirty data.
> >
> >Can you check if transactions are still getting lost in that setup? If
> >so (I kind of expect they will be) we may have to do a bit of
> >blktracing, but that'll really narrow down the possibilities.
> >
> 
> Yes, the most recent transactions are still lost.

Think I figured out what's going on. Just had a chat with another kernel
dev and figured out the flaw in my logic :P

This is going to take some thought to fix, though it shouldn't be much
code. I'll let you know when I think I have a fix.