Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757427Ab3EUCZH (ORCPT ); Mon, 20 May 2013 22:25:07 -0400 Received: from plane.gmane.org ([80.91.229.3]:38581 "EHLO plane.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755340Ab3EUCZE (ORCPT ); Mon, 20 May 2013 22:25:04 -0400 X-Injected-Via-Gmane: http://gmane.org/ To: linux-kernel@vger.kernel.org From: Duncan <1i5t5.duncan@cox.net> Subject: Re: [RFC PATCH v1 0/5] BTRFS hot relocation support Date: Tue, 21 May 2013 02:22:34 +0000 (UTC) Message-ID: References: <1369062687-23544-1-git-send-email-zwu.kernel@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Complaints-To: usenet@ger.gmane.org X-Gmane-NNTP-Posting-Host: ip68-231-22-224.ph.ph.cox.net User-Agent: Pan/0.140 (Chocolate Salty Balls; GIT b00f96e /usr/src/portage/src/egit-src/pan2) Cc: linux-btrfs@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2491 Lines: 43 zwu.kernel posted on Mon, 20 May 2013 23:11:22 +0800 as excerpted: > The patchset is trying to introduce hot relocation support > for BTRFS. In hybrid storage environment, when the data in rotating disk > get hot, it can be relocated to nonrotating disk by BTRFS hot relocation > support automatically; also, if nonrotating disk ratio exceed its upper > threshold, the data which get cold can be looked up and relocated to > rotating disk to make more space in nonrotating disk at first, and then > the data which get hot will be relocated to nonrotating disk > automatically. One advantage of a filesystem implementation, as opposed to bcache or dmcache, is arguably a corner-case, but it's /my/ corner-case, so... I run an intr*-less (I guess technically, empty initramfs) monolithic- kernel boot, using the kernel commandline root= and (formerly) md= and related logic to choose/assemble/mount root directly from the kernel command line via bootloader (grub2). Thus, any user-space-required-to- mount-root is out, since I don't have an initr* and thus no early userspace. That means both lvm2 and dmcache (AFAIK) are out. I'm not sure about bcache, but it has other negatives, particularly against btrfs- raid-1 and I'd guess md/raid-1 as well. Much like md before it, btrfs, while normally requiring the user-space- required device-scan to properly handle multiple devices, has kernel- command-line options that allow direct kernel multi-device assembly without the help of early-userspace/initr*. So in-btrfs hot-relocation support building on the existing kernel- command-line multi-device assembly options would definitely be welcomed by all us no-initr* folks looking at SSDs but not able to afford them for /everything/ just yet. =:^) (That said, even if accepted, your solution's a bit late for my own current needs, but there's surely going to be others hitting the same issue in a few kernel cycles when your patches could be mainline btrfs, and having the option at my next upgrade cycle say a couple years out would be very nice, indeed. =:^) -- Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/