From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx104.postini.com [74.125.245.104]) by kanga.kvack.org (Postfix) with SMTP id 206646B004F for ; Thu, 26 Jan 2012 11:59:47 -0500 (EST) References: <20120124203936.GC20650@quack.suse.cz> <20120125032932.GA7150@localhost> <1327502034.2720.23.camel@menhir> <1327509623.2720.52.camel@menhir> <1327512727.2776.52.camel@dabdike.int.hansenpartnership.com> <1327516668.7168.7.camel@dabdike.int.hansenpartnership.com> <20120125200613.GH15866@shiny> <20120125224614.GM30782@redhat.com> In-Reply-To: Mime-Version: 1.0 (1.0) Content-Type: text/plain; charset=us-ascii Message-Id: <10715842-8E51-40A5-8C28-AD8B1090645D@dilger.ca> Content-Transfer-Encoding: quoted-printable From: Andreas Dilger Subject: Re: [Lsf-pc] [dm-devel] [LSF/MM TOPIC] a few storage topics Date: Thu, 26 Jan 2012 10:00:04 -0700 Sender: owner-linux-mm@kvack.org List-ID: To: "Loke, Chetan" Cc: Andrea Arcangeli , Chris Mason , James Bottomley , Steven Whitehouse , Andreas Dilger , Jan Kara , Mike Snitzer , "" , "" , "" , Christoph Hellwig , "" , Jeff Moyer , Wu Fengguang , Boaz Harrosh , "" , "" , "Darrick J.Wong" On 2012-01-26, at 9:40, "Loke, Chetan" wrote: > And 'maybe' for adaptive RA just increase the RA-blocks by '1'(or some > N) over period of time. No more smartness. A simple 10 line function is > easy to debug/maintain. That is, a scaled-down version of > ramp-up/ramp-down. Don't go crazy by ramping-up/down after every RA(like > SCSI LLDD madness). Wait for some event to happen. Doing 1-block readahead increments is a performance disaster on RAID-5/6. Th= at means you seek all the disks, but use only a fraction of the data that th= e controller read internally and had to parity check. It makes more sense to keep the read units the same size as write units (1 M= B or as dictated by RAID geometry) that the filesystem is also hopefully usi= ng for allocation. When doing a readahead it should fetch the whole chunk a= t one time, then not do another until it needs another full chunk. Cheers, Andreas= -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org