linux-ext4 - Re: [PATCH v7 0/5] Introduce provisioning primitives

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Date:   Fri, 9 Jun 2023 10:10:13 +1000
From:   Dave Chinner <david@...morbit.com>
To:     "Martin K. Petersen" <martin.petersen@...cle.com>
Cc:     Sarthak Kukreti <sarthakkukreti@...omium.org>,
        Mike Snitzer <snitzer@...nel.org>,
        Joe Thornber <thornber@...hat.com>,
        Jens Axboe <axboe@...nel.dk>,
        Christoph Hellwig <hch@...radead.org>,
        Theodore Ts'o <tytso@....edu>, dm-devel@...hat.com,
        "Michael S. Tsirkin" <mst@...hat.com>,
        "Darrick J. Wong" <djwong@...nel.org>,
        Brian Foster <bfoster@...hat.com>,
        Bart Van Assche <bvanassche@...gle.com>,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        Joe Thornber <ejt@...hat.com>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
        Jason Wang <jasowang@...hat.com>,
        Alasdair Kergon <agk@...hat.com>
Subject: Re: [PATCH v7 0/5] Introduce provisioning primitives

On Wed, Jun 07, 2023 at 10:03:40PM -0400, Martin K. Petersen wrote:
> 
> Dave,
> 
> > Possibly unintentionally, I didn't call it REQ_OP_PROVISION but that's
> > what I intended - the operation does not contain data at all. It's an
> > operation like REQ_OP_DISCARD or REQ_OP_WRITE_ZEROS - it contains a
> > range of sectors that need to be provisioned (or discarded), and
> > nothing else.
> 
> Yep. That's also how SCSI defines it. The act of provisioning a block
> range is done through an UNMAP command using a special flag. All it does
> is pin down those LBAs so future writes to them won't result in ENOSPC.

*nod*

That I knew, and it's one of the reasons I'd like the filesystem <->
block layer provisioning model to head in this direction. i.e. we
don't have to do anything special to enable routing of provisioning
requests to hardware and/or remote block storage devices (e.g.
ceph-rbd, nbd, etc). Hence "external" devices can provide the same
guarantees as a native software-only block device implementations
like dm-thinp can provide and everything gets just that little bit
better behaved...

Cheers,

Dave.

-- 
Dave Chinner
david@...morbit.com