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Re: [dm-devel] [PATCH UPDATED 4/5] md: implment REQ_FLUSH/FUA support

On Wed, 25 Aug 2010 13:22:26 +0200
Tejun Heo <tj kernel org> wrote:

> This patch converts md to support REQ_FLUSH/FUA instead of now
> deprecated REQ_HARDBARRIER.  In the core part (md.c), the following
> changes are notable.
> * Unlike REQ_HARDBARRIER, REQ_FLUSH/FUA don't interfere with
>   processing of other requests and thus there is no reason to mark the
>   queue congested while FLUSH/FUA is in progress.
> * REQ_FLUSH/FUA failures are final and its users don't need retry
>   logic.  Retry logic is removed.
> * Preflush needs to be issued to all member devices but FUA writes can
>   be handled the same way as other writes - their processing can be
>   deferred to request_queue of member devices.  md_barrier_request()
>   is renamed to md_flush_request() and simplified accordingly.
> For linear, raid0 and multipath, the core changes are enough.  raid1,
> 5 and 10 need the following conversions.
> * raid1: Handling of FLUSH/FUA bio's can simply be deferred to
>   request_queues of member devices.  Barrier related logic removed.
> * raid5: Queue draining logic dropped.  FUA bit is propagated through
>   biodrain and stripe resconstruction such that all the updated parts
>   of the stripe are written out with FUA writes if any of the dirtying
>   writes was FUA.  preread_active_stripes handling in make_request()
>   is updated as suggested by Neil Brown.
> * raid10: FUA bit needs to be propagated to write clones.
> linear, raid0, 1, 5 and 10 tested.
> Signed-off-by: Tejun Heo <tj kernel org>
> Cc: Neil Brown <neilb suse de>
> ---
> Rebased on top of -rc2 and updated as suggested.  Can you please
> review and ack it?

Reviewed-by: NeilBrown <neilb suse de>



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