linux-kernel - Re: [PATCH 1/6] block: add support for carrying a stream ID in a bio

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Date:	Tue, 24 Mar 2015 18:11:10 +0100
From:	Matias Bjørling <m@...rling.me>
To:	Jens Axboe <axboe@...com>, axboe@...nel.dk,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
CC:	ming.l@....samsung.com
Subject: Re: [PATCH 1/6] block: add support for carrying a stream ID in a
 bio

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.

Thanks,
Matias
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