From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756182AbbCXR1D (ORCPT ); Tue, 24 Mar 2015 13:27:03 -0400 Received: from mail-ig0-f177.google.com ([209.85.213.177]:33466 "EHLO mail-ig0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755106AbbCXR04 (ORCPT ); Tue, 24 Mar 2015 13:26:56 -0400 Message-ID: <55119E5E.6020405@kernel.dk> Date: Tue, 24 Mar 2015 11:26:54 -0600 From: Jens Axboe User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 MIME-Version: 1.0 To: =?windows-1252?Q?Matias_Bj=F8rling?= , Jens Axboe , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org CC: ming.l@ssi.samsung.com Subject: Re: [PATCH 1/6] block: add support for carrying a stream ID in a bio References: <1427210823-5283-1-git-send-email-axboe@fb.com> <1427210823-5283-2-git-send-email-axboe@fb.com> <55119AAE.9030202@bjorling.me> In-Reply-To: <55119AAE.9030202@bjorling.me> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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