> -----Original Message----- > From: Jens Axboe [mailto:axboe@xxxxxxxxx] > Sent: Tuesday, March 24, 2015 10:27 AM > To: Matias Bjørling; Jens Axboe; linux-kernel@xxxxxxxxxxxxxxx; linux- > fsdevel@xxxxxxxxxxxxxxx > Cc: Ming Lin-SSI > 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. Can we use 8 bits at least? I'll test performance with 16 streams. > > -- > 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
