Messages in this thread | | | Date | Tue, 24 Mar 2015 11:26:54 -0600 | From | Jens Axboe <> | Subject | Re: [PATCH 1/6] block: add support for carrying a stream ID in a bio |
| |
On 03/24/2015 11:11 AM, Matias Bjørling wrote: > On 03/24/2015 04:26 PM, Jens Axboe wrote: >> The top bits of bio->bi_flags are reserved for keeping the >> allocation pool, set aside the next four bits for carrying >> a stream ID. That leaves us with support for 15 streams, >> 0 is reserved as a "stream not set" value. > > 15 streams seem very limited. Can this be extended? e.g. 16 bits. > > 15 streams is enough for 1-4 applications. More, and applications starts > to fight over the same stream id's, leading them to place different age > data in same flash blocks and push us back to square one. > > I understand that Samsung multi-stream SSD supports a limited amount of > streams, more advance implementations should provide higher limits.
Pushing it higher is not a big deal as far as the implementation goes, though 16 bits might be stealing a bit too much space for this. On 32-bit archs, we have 18 bits currently free that we can abuse. The Samsung device supports 16 streams. That's honestly a lot more than I would expect most devices to support in hardware, 16 is a lot of open erase blocks and write append points. Obviously the open channel effort would make that more feasible, though.
-- Jens Axboe
| |