From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Fedyk Subject: Prereading block device doesn't help filesystems Date: Tue, 3 Jun 2003 10:49:35 -0700 Message-ID: <20030603174935.GA4044@matchmail.com> References: <20030529054511.GA30925@namesys.com> <3EDB9910.7040005@namesys.com> <1054584035.21053.65.camel@rode> <20030603053336.GC8667@namesys.com> Mime-Version: 1.0 Return-path: list-help: list-unsubscribe: list-post: Errors-To: flx@namesys.com Content-Disposition: inline In-Reply-To: <20030603053336.GC8667@namesys.com> List-Id: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Oleg Drokin Cc: Jeff Breidenbach , Hans Reiser , reiserfs-list@namesys.com On Tue, Jun 03, 2003 at 09:33:36AM +0400, Oleg Drokin wrote: > (e.g. dd if=/dev/hdb1 /dev/zero bs=1024k count=500 (replace 500 with the half of your RAM > in megabytes) and you have large enough RAM, there is a chance that this will cache > enough data to keep stuff moving more quickly. That won't work either. Basically you're copying the data into buffer cache, and the page cache won't be able to pick it up, so you're going to read from the disk twice. Even with Andrea's buffercache in pagecache from 2.4.10 it doesn't do the aliasing IIRC. And there were some long threads where Linus said he wouldn't accept patches to do the aliasing either. Don't know if he has changed his mind in 2.5 though...