Messages in this thread | | | Date | Tue, 24 Mar 2015 15:48:56 -0600 | From | Jens Axboe <> | Subject | Re: [PATCH RFC] Support for write stream IDs |
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On 03/24/2015 03:46 PM, Ming Lin-SSI wrote: >> -----Original Message----- >> From: Jens Axboe [mailto:axboe@kernel.dk] >> Sent: Tuesday, March 24, 2015 10:08 AM >> To: Jeff Moyer; Jens Axboe >> Cc: linux-kernel@vger.kernel.org; linux-fsdevel@vger.kernel.org; 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@fb.com> 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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