From: Rob Landley Subject: Re: [patch] rewrite rd Date: Tue, 4 Dec 2007 01:55:17 -0600 Message-ID: <200712040155.21124.rob@landley.net> References: <20071204042628.GA26636@wotan.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Cc: Linux Kernel Mailing List , linux-fsdevel@vger.kernel.org, Christian Borntraeger , "Eric W. Biederman" , Andrew Morton , Jens Axboe To: Nick Piggin Return-path: Received: from static-71-162-243-5.phlapa.fios.verizon.net ([71.162.243.5]:59122 "EHLO grelber.thyrsus.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751288AbXLDHza (ORCPT ); Tue, 4 Dec 2007 02:55:30 -0500 In-Reply-To: <20071204042628.GA26636@wotan.suse.de> Content-Disposition: inline Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Monday 03 December 2007 22:26:28 Nick Piggin wrote: > There is one slight downside -- direct block device access and filesystem > metadata access goes through an extra copy and gets stored in RAM twice. > However, this downside is only slight, because the real buffercache of the > device is now reclaimable (because we're not playing crazy games with it), > so under memory intensive situations, footprint should effectively be the > same -- maybe even a slight advantage to the new driver because it can also > reclaim buffer heads. For the embedded world, initramfs has pretty much rendered initrd obsolete, and that was the biggest user of the ramdisk code I know of. Beyond that, loopback mounts give you more flexible transient block devices than ramdisks do. (In fact, ramdisks are such an amazing pain to use/size/free that if I really needed something like that I'd just make a loopback mount in a ramfs instance.) Embedded users who still want a block interface for memory are generally trying to use a cramfs or squashfs image out of ROM or flash, although there are flash-specific filesystems for this and I dunno if they're actually mounting /dev/mem at an offset or something (md? losetup -o? Beats me, I haven't tried that myself yet...) Rob -- "One of my most productive days was throwing away 1000 lines of code." - Ken Thompson.