From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from syrinx.knorrie.org ([82.94.188.77]:46010 "EHLO syrinx.knorrie.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1426904AbdDVUVd (ORCPT ); Sat, 22 Apr 2017 16:21:33 -0400 Subject: Re: Experiences with metadata balance/convert To: Chris Murphy References: <78d61749-ec9c-1cc3-196f-5330489e2b3e@mendix.com> Cc: "linux-btrfs@vger.kernel.org" From: Hans van Kranenburg Message-ID: <838ab05f-094f-0c97-034f-e53e8cd374b7@mendix.com> Date: Sat, 22 Apr 2017 22:21:30 +0200 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 04/22/2017 06:45 PM, Chris Murphy wrote: > On Fri, Apr 21, 2017 at 4:26 AM, Hans van Kranenburg > wrote: > >> >> == Thinking out of the box == >> >> Technically, converting from DUP to single could also mean: >> * Flipping one bit in the block group type flags to 0 for each block >> group item >> * Flipping one bit in the chunk type flags and removing 1 stripe struct >> for each metadata chunk item >> * Removing the >> * Anything else? > > [...] > Such a prune would > need to write out new chunk and dev trees, and then whatever nodes end > up pointing to those, maybe it's just the super blocks. Or just use the existing offline tree plumbing code to remove some items and insert some replacement ones. >> How feasible would it be to write btrfs-progs style conversion to do this? > > I can pretty much say it's not just a bit flip change because at the > very least you've got new CRCs to write for any changed node. The tree plumbing will take care of that, I was not planning to hexedit it. > [...] I was actually thinking about writing a C extension for python-btrfs that gives me access to the building blocks that are present inside the btrfs-progs code, so that the 'heavy lifting' can be done there, and so that I can just easily script opening a filesystem and then doing tree changes, inserting and removing some tree items, even interactively. ;-) -- Hans van Kranenburg