linux-kernel - Re: [PATCH 23/41] dm: implement REQ_FLUSH/FUA support for bio-based dm

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Message-ID: <20100903123617.GA23812@redhat.com>
Date:	Fri, 3 Sep 2010 08:36:18 -0400
From:	Mike Snitzer <snitzer@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	jaxboe@...ionio.com, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-ide@...r.kernel.org, linux-raid@...r.kernel.org,
	dm-devel@...hat.com, hch@....de, konishi.ryusuke@....ntt.co.jp,
	James.Bottomley@...e.de, tytso@....edu, chris.mason@...cle.com,
	swhiteho@...hat.com, vst@...b.net, jack@...e.cz,
	rwheeler@...hat.com, hare@...e.de, neilb@...e.de,
	rusty@...tcorp.com.au, mst@...hat.com, k-ueda@...jp.nec.com,
	mpatocka@...hat.com
Subject: Re: [PATCH 23/41] dm: implement REQ_FLUSH/FUA support for bio-based
 dm

On Fri, Sep 03 2010 at  6:29am -0400,
Tejun Heo <tj@...nel.org> wrote:

> This patch converts bio-based dm to support REQ_FLUSH/FUA instead of
> now deprecated REQ_HARDBARRIER.
> 
> * -EOPNOTSUPP handling logic dropped.
> 
> * Preflush is handled as before but postflush is dropped and replaced
>   with passing down REQ_FUA to member request_queues.  This replaces
>   one array wide cache flush w/ member specific FUA writes.
> 
> * __split_and_process_bio() now calls __clone_and_map_flush() directly
>   for flushes and guarantees all FLUSH bio's going to targets are zero
> `  length.
> 
> * It's now guaranteed that all FLUSH bio's which are passed onto dm
>   targets are zero length.  bio_empty_barrier() tests are replaced
>   with REQ_FLUSH tests.
> 
> * Empty WRITE_BARRIERs are replaced with WRITE_FLUSHes.
> 
> * Dropped unlikely() around REQ_FLUSH tests.  Flushes are not unlikely
>   enough to be marked with unlikely().
> 
> * Block layer now filters out REQ_FLUSH/FUA bio's if the request_queue
>   doesn't support cache flushing.  Advertise REQ_FLUSH | REQ_FUA
>   capability.
> 
> * Request based dm isn't converted yet.  dm_init_request_based_queue()
>   resets flush support to 0 for now.  To avoid disturbing request
>   based dm code, dm->flush_error is added for bio based dm while
>   requested based dm continues to use dm->barrier_error.
> 
> Lightly tested linear, stripe, raid1, snap and crypt targets.  Please
> proceed with caution as I'm not familiar with the code base.

Reviewed-by: Mike Snitzer <snitzer@...hat.com>

Mikulas and/or Alasdair won't be able to review this until next week.
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