From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Phillips Subject: Re: Tux3 Report: How fast can we fail? Date: Wed, 13 May 2015 15:07:12 -0700 Message-ID: <5553CB10.70407@phunq.net> References: <8f886f13-6550-4322-95be-93244ae61045@phunq.net> <55523C88.9080809@phunq.net> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: linux-fsdevel@vger.kernel.org, tux3@tux3.org, OGAWA Hirofumi To: linux-kernel@vger.kernel.org Return-path: Received: from mail.phunq.net ([184.71.0.62]:40117 "EHLO starbase.phunq.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933971AbbEMWG6 (ORCPT ); Wed, 13 May 2015 18:06:58 -0400 In-Reply-To: <55523C88.9080809@phunq.net> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Addendum to that post... On 05/12/2015 10:46 AM, I wrote: > ...For example, we currently > overestimate the cost of a rewrite because we would need to go poking > around in btrees to do that more accurately. Fixing that will be quite > a bit of work... Ah no, I was wrong about that, it will not be a lot of work because it does not need to be done. Charging the full cost of a rewrite as if it is a new write is the right thing to do because we need to be sure the commit can allocate space to redirect the existing blocks before it frees the old ones. So that means there is no need for the front end to go delving into file metadata, ever, which is a relief because that would have been expensive and messy. Regards, Daniel