From: Chris Mason <chris.mason@oracle.com>
To: Edward Shishkin <edward.shishkin@gmail.com>
Cc: Mat <jackdachef@gmail.com>, LKML <linux-kernel@vger.kernel.org>,
linux-fsdevel@vger.kernel.org, Ric Wheeler <rwheeler@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
The development of BTRFS <linux-btrfs@vger.kernel.org>
Subject: Re: Btrfs: broken file system design (was Unbound(?) internal fragmentation in Btrfs)
Date: Fri, 18 Jun 2010 14:10:11 -0400 [thread overview]
Message-ID: <20100618181011.GS27466@think> (raw)
In-Reply-To: <4C1B9D4F.6010008@gmail.com>
On Fri, Jun 18, 2010 at 06:22:39PM +0200, Edward Shishkin wrote:
> Chris Mason wrote:
> >On Fri, Jun 18, 2010 at 05:05:46PM +0200, Edward Shishkin wrote:
> >>Chris Mason wrote:
> >>>On Fri, Jun 18, 2010 at 03:32:16PM +0200, Edward Shishkin wrote:
> >>>>Mat wrote:
> >>>>>On Thu, Jun 3, 2010 at 4:58 PM, Edward Shishkin <edward@redhat.com> wrote:
> >>>>>>Hello everyone.
> >>>>>>
> >>>>>>I was asked to review/evaluate Btrfs for using in enterprise
> >>>>>>systems and the below are my first impressions (linux-2.6.33).
> >>>>>>
> >>>>>>The first test I have made was filling an empty 659M (/dev/sdb2)
> >>>>>>btrfs partition (mounted to /mnt) with 2K files:
> >>>>>>
> >>>>>># for i in $(seq 1000000); \
> >>>>>>do dd if=/dev/zero of=/mnt/file_$i bs=2048 count=1; done
> >>>>>>(terminated after getting "No space left on device" reports).
> >>>>>>
> >>>>>># ls /mnt | wc -l
> >>>>>>59480
> >>>>>>
> >>>>>>So, I got the "dirty" utilization 59480*2048 / (659*1024*1024) = 0.17,
> >>>>>>and the first obvious question is "hey, where are other 83% of my
> >>>>>>disk space???" I looked at the btrfs storage tree (fs_tree) and was
> >>>>>>shocked with the situation on the leaf level. The Appendix B shows
> >>>>>>5 adjacent btrfs leafs, which have the same parent.
> >>>>>>
> >>>>>>For example, look at the leaf 29425664: "items 1 free space 3892"
> >>>>>>(of 4096!!). Note, that this "free" space (3892) is _dead_: any
> >>>>>>attempts to write to the file system will result in "No space left
> >>>>>>on device".
> >>>There are two easy ways to fix this problem. Turn off the inline
> >>>extents (max_inline=0) or allow splitting of the inline extents. I
> >>>didn't put in the splitting simply because the complexity was high while
> >>>the benefits were low (in comparison with just turning off the inline
> >>>extents).
> >>Hello, Chris. Thanks for response!
> >>I afraid that both ways won't fix the problem. Look at this leaf:
> >>
> >>[...]
> >>leaf 29425664 items 1 free space 3892 generation 8 owner 5
> >>fs uuid 50268d9d-2a53-4f4d-b3a3-4fbff74dd956
> >>chunk uuid 963ba49a-bb2b-48a3-9b35-520d857aade6
> >> item 0 key (320 XATTR_ITEM 3817753667) itemoff 3917 itemsize 78
> >> location key (0 UNKNOWN 0) type 8
> >> namelen 16 datalen 32 name: security.selinux
> >>[...]
> >>
> >>There is no inline extents, and what are you going to split here?
> >>All leafs must be at least a half filled, otherwise we loose all
> >>boundaries, which provides non-zero utilization..
> >
> >Right, there is no inline extent because we require them to fit entirely
> >in the leaf. So we end up with mostly empty leaves because the inline
> >item is large enough to make it difficult to push around but not large
> >enough to fill the leaf.
>
> How about left and right neighbors? They contain a lot of
> free space (1572 and 1901 respectively).
> I am not happy with the very fact of such shallow leafs which
> contain only one small (xattr) item..
Sure, the balancing can also be made more aggressive. This should be
very easy to fix.
-chris
next prev parent reply other threads:[~2010-06-18 18:10 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-06-03 14:58 Unbound(?) internal fragmentation in Btrfs Edward Shishkin
[not found] ` <AANLkTilKw2onQkdNlZjg7WVnPu2dsNpDSvoxrO_FA2z_@mail.gmail.com>
2010-06-18 8:03 ` Christian Stroetmann
2010-06-18 13:32 ` Btrfs: broken file system design (was Unbound(?) internal fragmentation in Btrfs) Edward Shishkin
2010-06-18 13:45 ` Daniel J Blueman
2010-06-18 16:50 ` Edward Shishkin
2010-06-23 23:40 ` Jamie Lokier
2010-06-24 3:43 ` Daniel Taylor
2010-06-24 4:51 ` Mike Fedyk
2010-06-24 22:06 ` Daniel Taylor
2010-06-25 9:15 ` Btrfs: broken file system design Andi Kleen
2010-06-25 18:58 ` Btrfs: broken file system design (was Unbound(?) internal fragmentation in Btrfs) Ric Wheeler
2010-06-26 5:18 ` Michael Tokarev
2010-06-26 11:55 ` Ric Wheeler
[not found] ` <57784.2001:5c0:82dc::2.1277555665.squirrel@www.tofubar.com>
2010-06-26 13:47 ` Ric Wheeler
2010-06-24 9:50 ` David Woodhouse
2010-06-18 18:15 ` Christian Stroetmann
2010-06-18 13:47 ` Chris Mason
2010-06-18 15:05 ` Edward Shishkin
[not found] ` <4C1B8B4A.9060308@gmail.com>
2010-06-18 15:10 ` Chris Mason
2010-06-18 16:22 ` Edward Shishkin
[not found] ` <4C1B9D4F.6010008@gmail.com>
2010-06-18 18:10 ` Chris Mason [this message]
2010-06-18 15:21 ` Christian Stroetmann
2010-06-18 15:22 ` Chris Mason
2010-06-18 15:56 ` Jamie Lokier
2010-06-18 19:25 ` Christian Stroetmann
2010-06-18 19:29 ` Edward Shishkin
2010-06-18 19:35 ` Chris Mason
2010-06-18 22:04 ` Balancing leaves when walking from top to down (was Btrfs:...) Edward Shishkin
[not found] ` <4C1BED56.9010300@redhat.com>
2010-06-18 22:16 ` Ric Wheeler
2010-06-19 0:03 ` Edward Shishkin
2010-06-21 13:15 ` Chris Mason
[not found] ` <20100621180013.GD17979@think>
2010-06-22 14:12 ` Edward Shishkin
2010-06-22 14:20 ` Chris Mason
2010-06-23 13:46 ` Edward Shishkin
[not found] ` <4C221049.501@gmail.com>
2010-06-23 23:37 ` Jamie Lokier
2010-06-24 13:06 ` Chris Mason
2010-06-30 20:05 ` Edward Shishkin
[not found] ` <4C2BA381.7040808@redhat.com>
2010-06-30 21:12 ` Chris Mason
2010-07-09 4:16 ` Chris Samuel
2010-07-09 20:30 ` Chris Mason
2010-06-23 23:57 ` Btrfs: broken file system design (was Unbound(?) internal fragmentation in Btrfs) Jamie Lokier
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