linux-kernel - Re: [dm-devel] [PATCH v4 00/13] support non power of 2 zoned devices

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Date:   Thu, 19 May 2022 07:34:43 +0000
From:   Johannes Thumshirn <Johannes.Thumshirn@....com>
To:     Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        Luis Chamberlain <mcgrof@...nel.org>
CC:     Theodore Ts'o <tytso@....edu>, Christoph Hellwig <hch@....de>,
        Pankaj Raghav <p.raghav@...sung.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "pankydev8@...il.com" <pankydev8@...il.com>,
        "gost.dev@...sung.com" <gost.dev@...sung.com>,
        "jiangbo.365@...edance.com" <jiangbo.365@...edance.com>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "dm-devel@...hat.com" <dm-devel@...hat.com>,
        "dsterba@...e.com" <dsterba@...e.com>,
        "linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>
Subject: Re: [dm-devel] [PATCH v4 00/13] support non power of 2 zoned devices

On 19/05/2022 05:19, Damien Le Moal wrote:
> On 5/19/22 12:12, Luis Chamberlain wrote:
>> On Thu, May 19, 2022 at 12:08:26PM +0900, Damien Le Moal wrote:
>>> On 5/18/22 00:34, Theodore Ts'o wrote:
>>>> On Tue, May 17, 2022 at 10:10:48AM +0200, Christoph Hellwig wrote:
>>>>> I'm a little surprised about all this activity.
>>>>>
>>>>> I though the conclusion at LSF/MM was that for Linux itself there
>>>>> is very little benefit in supporting this scheme.  It will massively
>>>>> fragment the supported based of devices and applications, while only
>>>>> having the benefit of supporting some Samsung legacy devices.
>>>>
>>>> FWIW,
>>>>
>>>> That wasn't my impression from that LSF/MM session, but once the
>>>> videos become available, folks can decide for themselves.
>>>
>>> There was no real discussion about zone size constraint on the zone
>>> storage BoF. Many discussions happened in the hallway track though.
>>
>> Right so no direct clear blockers mentioned at all during the BoF.
> 
> Nor any clear OK.

So what about creating a device-mapper target, that's taking npo2 drives and
makes them po2 drives for the FS layers? It will be very similar code to 
dm-linear.

After all zoned support for FSes started with a device-mapper (dm-zoned) and 
as the need for a more integrated solution arose, it changed into natiive
support.

And all that is there is simple arithmetic and a bio_clone(), if this is the
slowest part of the stack involving a FS like f2fs or btrfs I'm throwing a
round of anyone's favorite beverage at next year's LSFMM.

Byte,
	Johannes