linux-ext4 - Re: [PATCH RFC 1/3] block: Add support for REQ_OP_ASSIGN

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Message-ID: <3f2e341b-dea4-c5d0-8eb0-568b6ad2f17b@virtuozzo.com>
Date:   Thu, 19 Dec 2019 14:07:16 +0300
From:   Kirill Tkhai <ktkhai@...tuozzo.com>
To:     "Martin K. Petersen" <martin.petersen@...cle.com>, axboe@...nel.dk
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-ext4@...r.kernel.org, tytso@....edu,
        adilger.kernel@...ger.ca, ming.lei@...hat.com, osandov@...com,
        jthumshirn@...e.de, minwoo.im.dev@...il.com, damien.lemoal@....com,
        andrea.parri@...rulasolutions.com, hare@...e.com, tj@...nel.org,
        ajay.joshi@....com, sagi@...mberg.me, dsterba@...e.com,
        chaitanya.kulkarni@....com, bvanassche@....org,
        dhowells@...hat.com, asml.silence@...il.com
Subject: Re: [PATCH RFC 1/3] block: Add support for REQ_OP_ASSIGN_RANGE
 operation

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