From: Chris Mason <email@example.com> To: Edward Shishkin <firstname.lastname@example.org> Cc: Mat <email@example.com>, LKML <firstname.lastname@example.org>, email@example.com, Ric Wheeler <firstname.lastname@example.org>, Andrew Morton <email@example.com>, Linus Torvalds <firstname.lastname@example.org>, The development of BTRFS <email@example.com> 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.firstname.lastname@example.org> 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 <email@example.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::firstname.lastname@example.org> 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.email@example.com> 2010-06-18 15:10 ` Chris Mason 2010-06-18 16:22 ` Edward Shishkin [not found] ` <4C1B9D4F.firstname.lastname@example.org> 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.email@example.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.firstname.lastname@example.org> 2010-06-23 23:37 ` Jamie Lokier 2010-06-24 13:06 ` Chris Mason 2010-06-30 20:05 ` Edward Shishkin [not found] ` <4C2BA381.email@example.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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