[dm-devel] [PATCH] staging: writeboost: Add dm-writeboost

[Joe Thornber]

On Wed, Dec 10, 2014 at 10:31:31PM +0900, Akira Hayakawa wrote:
> Joe,
> 
> > So you copy the bio payload to a different block of ram and then
> > complete the bio?  Or does the rambuf refer to the bio payload
> > directly?
> Good question.
> The answer is, copy the data (got by bio_data(bio)) to rambuf once
> and ack if it's not barrier things.
> It would be nice if data in rambuf points to bio payload but it now copies
> because bio payload can be reused after completion. Am I right?
> Is there a way of eliminate memory copying?

You *have* to eliminate this memory copying.  Remap the bios to the
relevant portion of your log, and don't complete them until you log
chunk is coherent.