> -----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. Thanks, Ming > > -- > Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
