[dm-devel] [PATCH UPDATED 4/5] dm: implement REQ_FLUSH/FUA support for request-based dm
Mikulas Patocka
mpatocka at redhat.com
Wed Sep 1 12:12:52 UTC 2010
On Wed, 1 Sep 2010, Tejun Heo wrote:
> Hello,
>
> On 09/01/2010 12:31 PM, Mikulas Patocka wrote:
> > 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.
>
> Unfortunately, it doesn't work that way. The current dm
> implementation depends on block layer holding the queue while a
> barrier sequence is in progress which the new implementation doesn't
> do anymore (the whole point of this conversion BTW).
That may be true for request-based dm (I don't know).
But bio-based dm doesn't depend on it, I wrote it and I didn't rely on
that.
Mikulas
> Thanks.
>
> --
> tejun
>
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