From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.fusionio.com ([66.114.96.31]:40816 "EHLO mx2.fusionio.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751280Ab2IMMhX (ORCPT ); Thu, 13 Sep 2012 08:37:23 -0400 Date: Thu, 13 Sep 2012 08:37:20 -0400 From: Josef Bacik To: Liu Bo CC: Josef Bacik , "linux-btrfs@vger.kernel.org" Subject: Re: [PATCH] Btrfs: delay block group item insertion Message-ID: <20120913123720.GB12994@localhost.localdomain> References: <1347473053-3158-1-git-send-email-jbacik@fusionio.com> <20120913013205.GA12929@liubo> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" In-Reply-To: <20120913013205.GA12929@liubo> Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Wed, Sep 12, 2012 at 07:32:05PM -0600, Liu Bo wrote: > On Wed, Sep 12, 2012 at 02:04:13PM -0400, Josef Bacik wrote: > > So we have lots of places where we try to preallocate chunks in order to > > make sure we have enough space as we make our allocations. This has > > historically meant that we're constantly tweaking when we should allocate a > > new chunk, and historically we have gotten this horribly wrong so we way > > over allocate either metadata or data. To try and keep this from happening > > we are going to make it so that the block group item insertion is done out > > of band at the end of a transaction. This will allow us to create chunks > > even if we are trying to make an allocation for the extent tree. With this > > patch my enospc tests run faster (didn't expect this) and more efficiently > > use the disk space (this is what I wanted). Thanks, > > > > I'm afraid this does not perform good enough in normal case, here is the > compilebench test: > > # cat btrfs-makej/result-4k > intial create total runs 30 avg 51.99 MB/s (user 0.50s sys 0.85s) > compile total runs 30 avg 98.45 MB/s (user 0.12s sys 0.38s) > read compiled tree total runs 3 avg 19.89 MB/s (user 1.55s sys 3.07s) > delete compiled tree total runs 30 avg 12.15 seconds (user 0.66s sys 2.15s) > > # cat btrfs-josef-makej/result > intial create total runs 30 avg 49.79 MB/s (user 0.52s sys 0.87s) > compile total runs 30 avg 70.01 MB/s (user 0.14s sys 0.44s) > read compiled tree total runs 3 avg 18.46 MB/s (user 1.57s sys 3.16s) > delete compiled tree total runs 30 avg 13.88 seconds (user 0.67s sys 2.18s) > > And the blktrace shows that it makes us do more seeks in create and > compile section. > > The patch overall looks clean and good though. > Yeah mostly what I'm looking for is more efficient metadata chunk allocation, and I expected it to have a performance impact somwhere (I just never hit one in my ENOSPC tests). This drop is within reason for me and I'm willing to eat a slight performance drop to not allocate an entire disk with metadata ;). Thanks, Josef