Re: [PATCH RFC 1/3] block: Add support for REQ_OP_ASSIGN_RANGE operation

From: Kirill Tkhai <ktkhai@virtuozzo.com>
To: "Martin K. Petersen" <martin.petersen@oracle.com>, axboe@kernel.dk
Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-ext4@vger.kernel.org, tytso@mit.edu,
	adilger.kernel@dilger.ca, 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, chaitanya.kulkarni@wdc.com,
	bvanassche@acm.org, dhowells@redhat.com, asml.silence@gmail.com
Subject: Re: [PATCH RFC 1/3] block: Add support for REQ_OP_ASSIGN_RANGE operation
Date: Thu, 19 Dec 2019 14:07:16 +0300	[thread overview]
Message-ID: <3f2e341b-dea4-c5d0-8eb0-568b6ad2f17b@virtuozzo.com> (raw)
In-Reply-To: <yq1woatc8zd.fsf@oracle.com>

Hi, Martin!

On 19.12.2019 06:03, Martin K. Petersen wrote:
> 
> Hi Kirill!
> 
>> The patch adds a new blkdev_issue_assign_range() primitive, which is
>> rather similar to existing blkdev_issue_{*} api.  Also, a new queue
>> limit.max_assign_range_sectors is added.
> 
> I am not so keen on the assign_range name. What's wrong with "allocate"?

REQ_OP_ALLOCATE_RANGE seemed for me as looking very long for the reviewers.
And I found that there is no an abbreviation of operations name in enum req_opf,
so REQ_OP_ALLOC_RANGE won't look good. Thus, I found a replacement.

But in case of REQ_OP_ALLOCATE_RANGE length is OK for people, there is no
a problem to choose it.

> But why introduce a completely new operation? Isn't this essentially a
> write zeroes with BLKDEV_ZERO_NOUNMAP flag set?
> 
> If the zeroing aspect is perceived to be a problem we could add a
> BLKDEV_ZERO_ALLOCATE flag (or BLKDEV_ZERO_ANCHOR since that's the
> terminology used in SCSI).

Hm. BLKDEV_ZERO_NOUNMAP is used in __blkdev_issue_write_zeroes() only.
So, do I understand right that we should the below two?:

1)Introduce a new flag BLKDEV_ZERO_ALLOCATE for blkdev_issue_write_zeroes().
2)Introduce a new flag REQ_NOZERO in enum req_opf.

Won't this confuse a reader that we have blkdev_issue_write_zeroes(),
which does not write zeroes sometimes? Maybe we should rename
blkdev_issue_write_zeroes() in some more generic name?

Thanks,
Kirill