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From: Christoph Hellwig <hch@infradead.org>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>,
	Christoph Hellwig <hch@infradead.org>,
	Kirill Tkhai <ktkhai@virtuozzo.com>,
	axboe@kernel.dk, bob.liu@oracle.com, agk@redhat.com,
	snitzer@redhat.com, dm-devel@redhat.com, song@kernel.org,
	tytso@mit.edu, adilger.kernel@dilger.ca,
	Chaitanya.Kulkarni@wdc.com, ming.lei@redhat.com, osandov@fb.com,
	jthumshirn@suse.de, minwoo.im.dev@gmail.com,
	damien.lemoal@wdc.com, andrea.parri@amarulasolutions.com,
	hare@suse.com, tj@kernel.org, ajay.joshi@wdc.com,
	sagi@grimberg.me, dsterba@suse.com, bvanassche@acm.org,
	dhowells@redhat.com, asml.silence@gmail.com,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v7 0/6] block: Introduce REQ_ALLOCATE flag for REQ_OP_WRITE_ZEROES
Date: Wed, 25 Mar 2020 09:32:23 -0700
Message-ID: <20200325163223.GA27156@infradead.org> (raw)
In-Reply-To: <20200325162656.GJ29351@magnolia>

On Wed, Mar 25, 2020 at 09:26:56AM -0700, Darrick J. Wong wrote:
> > That said, I do think that we have traditionally put emphasis on the
> > wrong part of these operations. All we ever talk about wrt. discard and
> > friends is the zeroing aspect. But I actually think that, semantically,
> > the act of allocating and deallocating blocks is more important. And
> > that zeroing is an optional second order effect of those operations. So
> > if we could go back in time and nuke multi-range DSM TRIM/UNMAP, I would
> > like to have REQ_OP_ALLOCATE/REQ_OP_DEALLOCATE with an optional REQ_ZERO
> > flag. I think that would be cleaner. I have a much easier time wrapping
> > my head around "allocate this block and zero it if you can" than "zero
> > this block and do not deallocate it". But maybe that's just me.
> 
> I'd love to transition to that.  My brain is not good at following all
> the inverse logic that NOUNMAP spread everywhere.  I have a difficult
> time following what the blockdev fallocate code does, which is sad since
> hch and I are the primary stuckees^Wmeddlers^Wauthors of that function. :/

I am very much against that for the following reason:

 - the current REQ_OP_DISCARD is purely a hint, and implementations can
   (and do) choose to ignore it
 - REQ_OP_WRITE_ZEROES is an actual data integrity operation with
   everything that entails

Going back to mixing these two will lead to a disaster sooner or later.

  reply index

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-13  7:39 Kirill Tkhai
2020-02-13  7:39 ` [PATCH v7 1/6] block: Add @flags argument to bdev_write_zeroes_sectors() Kirill Tkhai
2020-02-13  7:39 ` [PATCH v7 2/6] block: Pass op_flags into blk_queue_get_max_sectors() Kirill Tkhai
2020-02-13  7:39 ` [PATCH v7 3/6] block: Introduce blk_queue_get_max_write_zeroes_sectors() Kirill Tkhai
2020-02-13  7:39 ` [PATCH v7 4/6] block: Add support for REQ_ALLOCATE flag Kirill Tkhai
2020-02-13  7:39 ` [PATCH v7 5/6] block: Add blk_queue_max_allocate_sectors() Kirill Tkhai
2020-02-13  7:39 ` [PATCH v7 6/6] loop: Add support for REQ_ALLOCATE Kirill Tkhai
2020-02-13 18:11   ` Darrick J. Wong
2020-02-13 20:07     ` Kirill Tkhai
2020-02-13  7:55 ` [PATCH v7 0/6] block: Introduce REQ_ALLOCATE flag for REQ_OP_WRITE_ZEROES Kirill Tkhai
2020-03-06  9:11   ` Kirill Tkhai
2020-03-13 13:08     ` Kirill Tkhai
2020-03-19 10:28       ` Christoph Hellwig
2020-03-19 10:42         ` Kirill Tkhai
2020-03-19 13:03         ` Martin K. Petersen
2020-03-25 16:26           ` Darrick J. Wong
2020-03-25 16:32             ` Christoph Hellwig [this message]
2020-03-25 17:23               ` Martin K. Petersen
2020-03-26  9:29                 ` Christoph Hellwig
2020-03-26 14:34                   ` Martin K. Petersen
2020-03-26 14:45                     ` Christoph Hellwig
2020-03-26 16:48                       ` Chaitanya Kulkarni

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