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

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Message-ID: <4a8f0e1b-0acb-1ed4-8d7a-c9ba93fcfd02@opensource.wdc.com>
Date:   Fri, 20 May 2022 12:47:03 +0900
From:   Damien Le Moal <damien.lemoal@...nsource.wdc.com>
To:     Johannes Thumshirn <Johannes.Thumshirn@....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 5/19/22 16:34, Johannes Thumshirn wrote:
> 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.

+1

This will simplify the support for FSes, at least for the initial drop (if
accepted).

And more importantly, this will also allow addressing any potential
problem with user space breaking because of the non power of 2 zone size.

> 
> 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
> 


-- 
Damien Le Moal
Western Digital Research