[PATCH V2 0/2] nvme: Support for fused NVME_IOCTL_SUBMIT_IO

[Clay Mayers]

> From: Chaitanya Kulkarni <Chaitanya.Kulkarni at wdc.com>
> Sent: Monday, January 25, 2021 5:43 PM
> To: Clay Mayers <Clay.Mayers at kioxia.com>; linux-nvme at lists.infradead.org
> Cc: Keith Busch <kbusch at kernel.org>; Jens Axboe <axboe at fb.com>;
> Christoph Hellwig <hch at lst.de>; Sagi Grimberg <sagi at grimberg.me>
> Subject: Re: [PATCH V2 0/2] nvme: Support for fused
> NVME_IOCTL_SUBMIT_IO
> 
> On 1/25/21 12:03, clay.mayers at kioxia.com wrote:
> > Local pci device fused support is also necessary for NVMeOF targets to
> > support fused operation.
> Please explain the use case and the application of the NVMeOF fuse
> command feature.

NVMeOF devices are used to create disaggregated storage systems
where compute and storage are connected over a fabric.  Fused
compare/write can be used to arbitrate shared access to NVMeOF devices
w/o a central authority.

A specific example of how fused compare/write is used is the clustered
file system VMFS.  It uses the SCSI version of compare/write to manage
meta data on shared SAN systems.  File system meta data is updated
using locks stored on the storage media.  Those locks are grabbed using
fused compare/write operations as an atomic test & set.  VMFS originally
used device reserve, which is a courser gained locking mechanism but it
doesn't scale as well as an atomic test & set.