Re: [PATCH RFC] Support for write stream IDs

[Jens Axboe]

On 03/24/2015 03:46 PM, Ming Lin-SSI wrote:
> > -----Original Message-----
> > From: Jens Axboe [mailto:axboe@xxxxxxxxx]
> > Sent: Tuesday, March 24, 2015 10:08 AM
> > To: Jeff Moyer; Jens Axboe
> > Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-fsdevel@xxxxxxxxxxxxxxx; Ming Lin-
> > SSI
> > Subject: Re: [PATCH RFC] Support for write stream IDs
> >
> > On 03/24/2015 11:03 AM, Jeff Moyer wrote:
> > > Jens Axboe <axboe@xxxxxx> writes:
> > >
> > > > Hi,
> > > >
> > > > One of the things that exacerbates write amplification on flash based
> > > > devices is that fact that data with different lifetimes get grouped
> > > > together on media. Currently we have no interface that applications
> > > > can use to separate different types of writes. This patch set adds
> > > > support for that.
> > > >
> > > > The kernel has no knowledge of what stream ID is what. The idea is
> > > > that writes with identical stream IDs have similar life times, not
> > > > that stream ID 'X' has a shorter lifetime than stream ID 'X+1'.
> > > >
> > > > There are basically two interfaces that could be used for this. One
> > > > is fcntl, the other is fadvise. This patchset uses fadvise, with a
> > > > new POSIX_FADV_STREAMID hint. The 'offset' field is used to pass the
> > > > relevant stream ID. Switching to fcntl (with a SET/GET_STREAMID)
> > > > would be trivial.
> > > >
> > > > The patchset wires up the block parts, adds buffered and O_DIRECT
> > > > support, and modifies btrfs/xfs too. It should be trivial to extend
> > > > this to all other file systems, I just used xfs and btrfs for testing.
> > > >
> > > > No block drivers are wired up yet. Patches are against current -git.
> > >
> > > Can you give an idea of how the stream id would be communicated to the
> > > device?  NVMe doesn't appear to have any notion of a data stream ID.
> >
> > It doesn't have it, yet, completely. Ming Lin can expand on what it looks like
> > for the Samsung nvme devices. Current nvme does have vague support for it,
> > however. The write command does have bits for frequent vs infrequent vs
> > one-time writes.
>
> Samsung extended NVMe spec to add "stream control command" to open/close stream.
> And with small modification to the "Write command" to write to open stream.
>
> We are promoting the multi-stream spec to NVMe group.

Can you share the nvme spec proposal with us?

--
Jens Axboe

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