From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751842AbaLCPZt (ORCPT ); Wed, 3 Dec 2014 10:25:49 -0500 Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:48266 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751369AbaLCPZs (ORCPT ); Wed, 3 Dec 2014 10:25:48 -0500 Date: Wed, 3 Dec 2014 16:25:45 +0100 From: Pavel Machek To: Dave Chinner Cc: "Jason B. Akers" , linux-ide@vger.kernel.org, axboe@fb.com, dan.j.williams@intel.com, kapil.karkra@intel.com, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 0/5] Enable use of Solid State Hybrid Drives Message-ID: <20141203152544.GA21586@amd> References: <20141029180454.4879.75088.stgit@stg-AndroidDev-VirtualBox> <20141029201417.GK16186@dastard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141029201417.GK16186@dastard> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 2014-10-30 07:14:17, Dave Chinner wrote: > On Wed, Oct 29, 2014 at 11:23:38AM -0700, Jason B. Akers wrote: > > The following series enables the use of Solid State hybrid drives > > ATA standard 3.2 defines the hybrid information feature, which provides a means for the host driver to provide hints to the SSHDs to guide what to place on the SSD/NAND portion and what to place on the magnetic media. > > > > This implementation allows user space applications to provide the cache hints to the kernel using the existing ionice syscall. > > > > An application can pass a priority number coding up bits 11, 12, and 15 of the ionice command to form a 3 bit field that encodes the following priorities: > > OPRIO_ADV_NONE, > > IOPRIO_ADV_EVICT, /* actively discard cached data */ > > IOPRIO_ADV_DONTNEED, /* caching this data has little value */ > > IOPRIO_ADV_NORMAL, /* best-effort cache priority (default) */ > > IOPRIO_ADV_RESERVED1, /* reserved for future use */ > > IOPRIO_ADV_RESERVED2, > > IOPRIO_ADV_RESERVED3, > > IOPRIO_ADV_WILLNEED, /* high temporal locality */ > > > > For example the following commands from the user space will make dd IOs to be generated with a hint of IOPRIO_ADV_DONTNEED assuming the SSHD is /dev/sdc. > > > > ionice -c2 -n4096 dd if=/dev/zero of=/dev/sdc bs=1M count=1024 > > ionice -c2 -n4096 dd if=/dev/sdc of=/dev/null bs=1M count=1024 > > This looks to be the wrong way to implement per-IO priority > information. > > How does a filesystem make use of this to make sure it's > metadata ends up with IOPRIO_ADV_WILLNEED to store frequently > accessed metadata in flash. Conversely, journal writes need to > be issued with IOPRIO_ADV_DONTNEED so they don't unneceessarily > consume flash space as they are never-read IOs... Well, that makes sense, but we still want some kind of per-application priority. I'd like ~/.chromium directory cached in the SSD part, but I don't neccessarily want /data/backup directory cached in the SSD... Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html