From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: [PATCH 1/6] block: add support for carrying a stream ID in a bio Date: Tue, 24 Mar 2015 11:26:54 -0600 Message-ID: <55119E5E.6020405@kernel.dk> References: <1427210823-5283-1-git-send-email-axboe@fb.com> <1427210823-5283-2-git-send-email-axboe@fb.com> <55119AAE.9030202@bjorling.me> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: ming.l@ssi.samsung.com To: =?windows-1252?Q?Matias_Bj=F8rling?= , Jens Axboe , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Return-path: Received: from mail-ig0-f178.google.com ([209.85.213.178]:33466 "EHLO mail-ig0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755072AbbCXR04 (ORCPT ); Tue, 24 Mar 2015 13:26:56 -0400 Received: by ignm3 with SMTP id m3so55994125ign.0 for ; Tue, 24 Mar 2015 10:26:55 -0700 (PDT) In-Reply-To: <55119AAE.9030202@bjorling.me> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On 03/24/2015 11:11 AM, Matias Bj=F8rling 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 sta= rts > to fight over the same stream id's, leading them to place different a= ge > 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,=20 though 16 bits might be stealing a bit too much space for this. On=20 32-bit archs, we have 18 bits currently free that we can abuse. The=20 Samsung device supports 16 streams. That's honestly a lot more than I=20 would expect most devices to support in hardware, 16 is a lot of open=20 erase blocks and write append points. Obviously the open channel effort= =20 would make that more feasible, though. --=20 Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel= " in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html