Re: [dm-devel] [PATCH UPDATED 4/5] dm: implement REQ_FLUSH/FUA support for request-based dm

[Mikulas Patocka <mpatocka redhat com>]

On Mon, 30 Aug 2010, Mike Snitzer wrote:

> Hi,
> 
> On Mon, Aug 30 2010 at 11:45am -0400,
> Tejun Heo <tj kernel org> wrote:
> 
> > Here's a version w/ BUG_ON() added.  Once the queue hang issue is
> > tracked down, I'll refresh the whole series and repost.
> 
> When you next send out the refreshed series, could you cc dm-devel any
> patches that touch DM directly or block patches that are required to
> support DM?
> 
> It'd be great to cc Mikulas Patocka on those patches too (I cc'd him).
> Mikulas will be reviewing these DM patches now that we have something
> that works with your larger FLUSH+FUA patchset.
> 
> Thanks,
> Mike

My recommended approach to this (on non-request-based dm) is to simply let 
the current barrier infrastructure be as it is --- you don't need to 
change it now, you can simply map FUA write to barrier write and FLUSH to 
zero-data barrier --- and it won't cause any data corruption. It will just 
force unneeded I/O queue draining.

Once FLUSH+FUA interface is finalized and committed upstream, we can 
remove that I/O queue draining from dm to improve performance.

Mikulas