Am Sonntag, 28. Dezember 2014, 14:56:21 schrieb Martin Steigerwald: > Am Sonntag, 28. Dezember 2014, 14:40:32 schrieb Martin Steigerwald: > > Am Sonntag, 28. Dezember 2014, 14:00:19 schrieb Martin Steigerwald: > > > Am Samstag, 27. Dezember 2014, 14:55:58 schrieb Martin Steigerwald: > > > > Summarized at > > > > > > > > Bug 90401 - btrfs kworker thread uses up 100% of a Sandybridge core for minutes on random write into big file > > > > https://bugzilla.kernel.org/show_bug.cgi?id=90401 > > > > > > > > see below. This is reproducable with fio, no need for Windows XP in > > > > Virtualbox for reproducing the issue. Next I will try to reproduce with > > > > a freshly creating filesystem. > > > > > > > > > > > > Am Samstag, 27. Dezember 2014, 09:30:43 schrieb Hugo Mills: > > > > > On Sat, Dec 27, 2014 at 10:01:17AM +0100, Martin Steigerwald wrote: > > > > > > Am Freitag, 26. Dezember 2014, 14:48:38 schrieb Robert White: > > > > > > > On 12/26/2014 05:37 AM, Martin Steigerwald wrote: > > > > > > > > Hello! > > > > > > > > > > > > > > > > First: Have a merry christmas and enjoy a quiet time in these days. > > > > > > > > > > > > > > > > Second: At a time you feel like it, here is a little rant, but also a > > > > > > > > bug > > > > > > > > report: > > > > > > > > > > > > > > > > I have this on 3.18 kernel on Debian Sid with BTRFS Dual SSD RAID with > > > > > > > > space_cache, skinny meta data extents – are these a problem? – and > > > > > > > > > > > > > > > compress=lzo: > > > > > > > (there is no known problem with skinny metadata, it's actually more > > > > > > > efficient than the older format. There has been some anecdotes about > > > > > > > mixing the skinny and fat metadata but nothing has ever been > > > > > > > demonstrated problematic.) > > > > > > > > > > > > > > > merkaba:~> btrfs fi sh /home > > > > > > > > Label: 'home' uuid: b96c4f72-0523-45ac-a401-f7be73dd624a > > > > > > > > > > > > > > > > Total devices 2 FS bytes used 144.41GiB > > > > > > > > devid 1 size 160.00GiB used 160.00GiB path > > > > > > > > /dev/mapper/msata-home > > > > > > > > devid 2 size 160.00GiB used 160.00GiB path > > > > > > > > /dev/mapper/sata-home > > > > > > > > > > > > > > > > Btrfs v3.17 > > > > > > > > merkaba:~> btrfs fi df /home > > > > > > > > Data, RAID1: total=154.97GiB, used=141.12GiB > > > > > > > > System, RAID1: total=32.00MiB, used=48.00KiB > > > > > > > > Metadata, RAID1: total=5.00GiB, used=3.29GiB > > > > > > > > GlobalReserve, single: total=512.00MiB, used=0.00B > > > > > > > > > > > > > > This filesystem, at the allocation level, is "very full" (see below). > > > > > > > > > > > > > > > And I had hangs with BTRFS again. This time as I wanted to install tax > > > > > > > > return software in Virtualbox´d Windows XP VM (which I use once a year > > > > > > > > cause I know no tax return software for Linux which would be suitable > > > > > > > > for > > > > > > > > Germany and I frankly don´t care about the end of security cause all > > > > > > > > surfing and other network access I will do from the Linux box and I > > > > > > > > only > > > > > > > > run the VM behind a firewall). > > > > > > > > > > > > > > > And thus I try the balance dance again: > > > > > > > ITEM: Balance... it doesn't do what you think it does... > > > > > > > > > > > > > > "Balancing" is something you should almost never need to do. It is only > > > > > > > for cases of changing geometry (adding disks, switching RAID levels, > > > > > > > etc.) of for cases when you've radically changed allocation behaviors > > > > > > > (like you decided to remove all your VM's or you've decided to remove a > > > > > > > mail spool directory full of thousands of tiny files). > > > > > > > > > > > > > > People run balance all the time because they think they should. They are > > > > > > > _usually_ incorrect in that belief. > > > > > > > > > > > > I only see the lockups of BTRFS is the trees *occupy* all space on the > > > > > > device. > > > > > No, "the trees" occupy 3.29 GiB of your 5 GiB of mirrored metadata > > > > > space. What's more, balance does *not* balance the metadata trees. The > > > > > remaining space -- 154.97 GiB -- is unstructured storage for file > > > > > data, and you have some 13 GiB of that available for use. > > > > > > > > > > Now, since you're seeing lockups when the space on your disks is > > > > > all allocated I'd say that's a bug. However, you're the *only* person > > > > > who's reported this as a regular occurrence. Does this happen with all > > > > > filesystems you have, or just this one? > > > > > > > > > > > I *never* so far saw it lockup if there is still space BTRFS can allocate > > > > > > from to *extend* a tree. > > > > > > > > > > It's not a tree. It's simply space allocation. It's not even space > > > > > *usage* you're talking about here -- it's just allocation (i.e. the FS > > > > > saying "I'm going to use this piece of disk for this purpose"). > > > > > > > > > > > This may be a bug, but this is what I see. > > > > > > > > > > > > And no amount of "you should not balance a BTRFS" will make that > > > > > > perception go away. > > > > > > > > > > > > See, I see the sun coming out on a morning and you tell me "no, it > > > > > > doesn´t". Simply that is not going to match my perception. > > > > > > > > > > Duncan's assertion is correct in its detail. Looking at your space > > > > > > > > Robert's > > > > > > > > > usage, I would not suggest that running a balance is something you > > > > > need to do. Now, since you have these lockups that seem quite > > > > > repeatable, there's probably a lurking bug in there, but hacking > > > > > around with balance every time you hit it isn't going to get the > > > > > problem solved properly. > > > > > > > > > > I think I would suggest the following: > > > > > > > > > > - make sure you have some way of logging your dmesg permanently (use > > > > > a different filesystem for /var/log, or a serial console, or a > > > > > netconsole) > > > > > > > > > > - when the lockup happens, hit Alt-SysRq-t a few times > > > > > > > > > > - send the dmesg output here, or post to bugzilla.kernel.org > > > > > > > > > > That's probably going to give enough information to the developers > > > > > to work out where the lockup is happening, and is clearly the way > > > > > forward here. > > > > > > > > And I got it reproduced. *Perfectly* reproduced, I´d say. > > > > > > > > But let me run the whole story: > > > > > > > > 1) I downsized my /home BTRFS from dual 170 GiB to dual 160 GiB again. > > > > > > [… story of trying to reproduce with Windows XP defragmenting which was > > > unsuccessful as BTRFS still had free device space to allocate new chunks > > > from …] > > > > > > > But finally I got to: > > > > > > > > merkaba:~> date; btrfs fi sh /home ; btrfs fi df /home > > > > Sa 27. Dez 13:26:39 CET 2014 > > > > Label: 'home' uuid: [some UUID] > > > > Total devices 2 FS bytes used 152.83GiB > > > > devid 1 size 160.00GiB used 160.00GiB path /dev/mapper/msata-home > > > > devid 2 size 160.00GiB used 160.00GiB path /dev/mapper/sata-home > > > > > > > > Btrfs v3.17 > > > > Data, RAID1: total=154.97GiB, used=149.58GiB > > > > System, RAID1: total=32.00MiB, used=48.00KiB > > > > Metadata, RAID1: total=5.00GiB, used=3.26GiB > > > > GlobalReserve, single: total=512.00MiB, used=0.00B > > > > > > > > > > > > > > > > So I did, if Virtualbox can write randomly in a file, I can too. > > > > > > > > So I did: > > > > > > > > > > > > martin@merkaba:~> cat ssd-test.fio > > > > [global] > > > > bs=4k > > > > #ioengine=libaio > > > > #iodepth=4 > > > > size=4g > > > > #direct=1 > > > > runtime=120 > > > > filename=ssd.test.file > > > > > > > > [seq-write] > > > > rw=write > > > > stonewall > > > > > > > > [rand-write] > > > > rw=randwrite > > > > stonewall > > > > > > > > > > > > > > > > And got: > > > > > > > > ATOP - merkaba 2014/12/27 13:41:02 ----------- 10s elapsed > > > > PRC | sys 10.14s | user 0.38s | #proc 332 | #trun 2 | #tslpi 548 | #tslpu 0 | #zombie 0 | no procacct | > > > > CPU | sys 102% | user 4% | irq 0% | idle 295% | wait 0% | guest 0% | curf 3.10GHz | curscal 96% | > > > > cpu | sys 76% | user 0% | irq 0% | idle 24% | cpu001 w 0% | guest 0% | curf 3.20GHz | curscal 99% | > > > > cpu | sys 24% | user 1% | irq 0% | idle 75% | cpu000 w 0% | guest 0% | curf 3.19GHz | curscal 99% | > > > > cpu | sys 1% | user 1% | irq 0% | idle 98% | cpu002 w 0% | guest 0% | curf 3.00GHz | curscal 93% | > > > > cpu | sys 1% | user 1% | irq 0% | idle 98% | cpu003 w 0% | guest 0% | curf 3.00GHz | curscal 93% | > > > > CPL | avg1 0.82 | avg5 0.78 | avg15 0.99 | | csw 6233 | intr 12023 | | numcpu 4 | > > > > MEM | tot 15.5G | free 4.0G | cache 9.7G | buff 0.0M | slab 333.1M | shmem 206.6M | vmbal 0.0M | hptot 0.0M | > > > > SWP | tot 12.0G | free 11.7G | | | | | vmcom 3.4G | vmlim 19.7G | > > > > LVM | sata-home | busy 0% | read 8 | write 0 | KiB/w 0 | MBr/s 0.00 | MBw/s 0.00 | avio 0.12 ms | > > > > DSK | sda | busy 0% | read 8 | write 0 | KiB/w 0 | MBr/s 0.00 | MBw/s 0.00 | avio 0.12 ms | > > > > NET | transport | tcpi 16 | tcpo 16 | udpi 0 | udpo 0 | tcpao 1 | tcppo 1 | tcprs 0 | > > > > NET | network | ipi 16 | ipo 16 | ipfrw 0 | deliv 16 | | icmpi 0 | icmpo 0 | > > > > NET | lo ---- | pcki 16 | pcko 16 | si 2 Kbps | so 2 Kbps | erri 0 | erro 0 | drpo 0 | > > > > > > > > PID TID RUID EUID THR SYSCPU USRCPU VGROW RGROW RDDSK WRDSK ST EXC S CPUNR CPU CMD 1/2 > > > > 18079 - martin martin 2 9.99s 0.00s 0K 0K 0K 16K -- - R 1 100% fio > > > > 4746 - martin martin 2 0.01s 0.14s 0K 0K 0K 0K -- - S 2 2% konsole > > > > 3291 - martin martin 4 0.01s 0.11s 0K 0K 0K 0K -- - S 0 1% plasma-desktop > > > > 1488 - root root 1 0.03s 0.04s 0K 0K 0K 0K -- - S 0 1% Xorg > > > > 10036 - root root 1 0.04s 0.02s 0K 0K 0K 0K -- - R 2 1% atop > > > > > > > > while fio was just *laying* out the 4 GiB file. Yes, thats 100% system CPU > > > > for 10 seconds while allocatiing a 4 GiB file on a filesystem like: > > > > > > > > martin@merkaba:~> LANG=C df -hT /home > > > > Filesystem Type Size Used Avail Use% Mounted on > > > > /dev/mapper/msata-home btrfs 170G 156G 17G 91% /home > > > > > > > > where a 4 GiB file should easily fit, no? (And this output is with the 4 > > > > GiB file. So it was even 4 GiB more free before.) > > > > > > > > > > > > But it gets even more visible: > > > > > > > > martin@merkaba:~> fio ssd-test.fio > > > > seq-write: (g=0): rw=write, bs=4K-4K/4K-4K/4K-4K, ioengine=sync, iodepth=1 > > > > rand-write: (g=1): rw=randwrite, bs=4K-4K/4K-4K/4K-4K, ioengine=sync, iodepth=1 > > > > fio-2.1.11 > > > > Starting 2 processes > > > > Jobs: 1 (f=1): [_(1),w(1)] [19.3% done] [0KB/0KB/0KB /s] [0/0/0 iops] [eta 01m:57s] > > > > 0$ zsh 1$ zsh 2$ zsh 3-$ zsh 4$ zsh 5$* zsh > > > > > > > > > > > > yes, thats 0 IOPS. > > > > > > > > 0 IOPS and in zero IOPS. For minutes. > > > > > > > > > > > > > > > > And here is why: > > > > > > > > ATOP - merkaba 2014/12/27 13:46:52 ----------- 10s elapsed > > > > PRC | sys 10.77s | user 0.31s | #proc 334 | #trun 2 | #tslpi 548 | #tslpu 3 | #zombie 0 | no procacct | > > > > CPU | sys 108% | user 3% | irq 0% | idle 286% | wait 2% | guest 0% | curf 3.08GHz | curscal 96% | > > > > cpu | sys 72% | user 1% | irq 0% | idle 28% | cpu000 w 0% | guest 0% | curf 3.00GHz | curscal 93% | > > > > cpu | sys 19% | user 0% | irq 0% | idle 81% | cpu001 w 0% | guest 0% | curf 3.00GHz | curscal 93% | > > > > cpu | sys 11% | user 1% | irq 0% | idle 87% | cpu003 w 1% | guest 0% | curf 3.19GHz | curscal 99% | > > > > cpu | sys 6% | user 1% | irq 0% | idle 91% | cpu002 w 1% | guest 0% | curf 3.11GHz | curscal 97% | > > > > CPL | avg1 2.78 | avg5 1.34 | avg15 1.12 | | csw 50192 | intr 32379 | | numcpu 4 | > > > > MEM | tot 15.5G | free 5.0G | cache 8.7G | buff 0.0M | slab 332.6M | shmem 207.2M | vmbal 0.0M | hptot 0.0M | > > > > SWP | tot 12.0G | free 11.7G | | | | | vmcom 3.4G | vmlim 19.7G | > > > > LVM | sata-home | busy 5% | read 160 | write 11177 | KiB/w 3 | MBr/s 0.06 | MBw/s 4.36 | avio 0.05 ms | > > > > LVM | msata-home | busy 4% | read 28 | write 11177 | KiB/w 3 | MBr/s 0.01 | MBw/s 4.36 | avio 0.04 ms | > > > > LVM | sata-debian | busy 0% | read 0 | write 844 | KiB/w 4 | MBr/s 0.00 | MBw/s 0.33 | avio 0.02 ms | > > > > LVM | msata-debian | busy 0% | read 0 | write 844 | KiB/w 4 | MBr/s 0.00 | MBw/s 0.33 | avio 0.02 ms | > > > > DSK | sda | busy 5% | read 160 | write 10200 | KiB/w 4 | MBr/s 0.06 | MBw/s 4.69 | avio 0.05 ms | > > > > DSK | sdb | busy 4% | read 28 | write 10558 | KiB/w 4 | MBr/s 0.01 | MBw/s 4.69 | avio 0.04 ms | > > > > NET | transport | tcpi 35 | tcpo 33 | udpi 3 | udpo 3 | tcpao 2 | tcppo 1 | tcprs 0 | > > > > NET | network | ipi 38 | ipo 36 | ipfrw 0 | deliv 38 | | icmpi 0 | icmpo 0 | > > > > NET | eth0 0% | pcki 22 | pcko 20 | si 9 Kbps | so 2 Kbps | erri 0 | erro 0 | drpo 0 | > > > > NET | lo ---- | pcki 16 | pcko 16 | si 2 Kbps | so 2 Kbps | erri 0 | erro 0 | drpo 0 | > > > > > > > > PID TID RUID EUID THR SYSCPU USRCPU VGROW RGROW RDDSK WRDSK ST EXC S CPUNR CPU CMD 1/3 > > > > 14973 - root root 1 8.92s 0.00s 0K 0K 0K 144K -- - S 0 89% kworker/u8:14 > > > > 17450 - root root 1 0.86s 0.00s 0K 0K 0K 32K -- - R 3 9% kworker/u8:5 > > > > 788 - root root 1 0.25s 0.00s 0K 0K 128K 18880K -- - S 3 3% btrfs-transact > > > > 12254 - root root 1 0.14s 0.00s 0K 0K 64K 576K -- - S 2 1% kworker/u8:3 > > > > 17332 - root root 1 0.11s 0.00s 0K 0K 112K 1348K -- - S 2 1% kworker/u8:4 > > > > 3291 - martin martin 4 0.01s 0.09s 0K 0K 0K 0K -- - S 1 1% plasma-deskto > > > > > > > > > > > > > > > > > > > > ATOP - merkaba 2014/12/27 13:47:12 ----------- 10s elapsed > > > > PRC | sys 10.78s | user 0.44s | #proc 334 | #trun 3 | #tslpi 547 | #tslpu 3 | #zombie 0 | no procacct | > > > > CPU | sys 106% | user 4% | irq 0% | idle 288% | wait 1% | guest 0% | curf 3.00GHz | curscal 93% | > > > > cpu | sys 93% | user 0% | irq 0% | idle 7% | cpu002 w 0% | guest 0% | curf 3.00GHz | curscal 93% | > > > > cpu | sys 7% | user 0% | irq 0% | idle 93% | cpu003 w 0% | guest 0% | curf 3.01GHz | curscal 94% | > > > > cpu | sys 3% | user 2% | irq 0% | idle 94% | cpu000 w 0% | guest 0% | curf 3.00GHz | curscal 93% | > > > > cpu | sys 3% | user 2% | irq 0% | idle 95% | cpu001 w 0% | guest 0% | curf 3.00GHz | curscal 93% | > > > > CPL | avg1 3.33 | avg5 1.56 | avg15 1.20 | | csw 38253 | intr 23104 | | numcpu 4 | > > > > MEM | tot 15.5G | free 4.9G | cache 8.7G | buff 0.0M | slab 336.5M | shmem 207.2M | vmbal 0.0M | hptot 0.0M | > > > > SWP | tot 12.0G | free 11.7G | | | | | vmcom 3.4G | vmlim 19.7G | > > > > LVM | msata-home | busy 2% | read 0 | write 2337 | KiB/w 3 | MBr/s 0.00 | MBw/s 0.91 | avio 0.07 ms | > > > > LVM | sata-home | busy 2% | read 36 | write 2337 | KiB/w 3 | MBr/s 0.01 | MBw/s 0.91 | avio 0.07 ms | > > > > LVM | msata-debian | busy 1% | read 1 | write 1630 | KiB/w 4 | MBr/s 0.00 | MBw/s 0.65 | avio 0.03 ms | > > > > LVM | sata-debian | busy 0% | read 0 | write 1019 | KiB/w 4 | MBr/s 0.00 | MBw/s 0.41 | avio 0.02 ms | > > > > DSK | sdb | busy 2% | read 1 | write 2545 | KiB/w 5 | MBr/s 0.00 | MBw/s 1.45 | avio 0.07 ms | > > > > DSK | sda | busy 1% | read 36 | write 2461 | KiB/w 5 | MBr/s 0.01 | MBw/s 1.28 | avio 0.06 ms | > > > > NET | transport | tcpi 20 | tcpo 20 | udpi 1 | udpo 1 | tcpao 1 | tcppo 1 | tcprs 0 | > > > > NET | network | ipi 21 | ipo 21 | ipfrw 0 | deliv 21 | | icmpi 0 | icmpo 0 | > > > > NET | eth0 0% | pcki 5 | pcko 5 | si 0 Kbps | so 0 Kbps | erri 0 | erro 0 | drpo 0 | > > > > NET | lo ---- | pcki 16 | pcko 16 | si 2 Kbps | so 2 Kbps | erri 0 | erro 0 | drpo 0 | > > > > > > > > PID TID RUID EUID THR SYSCPU USRCPU VGROW RGROW RDDSK WRDSK ST EXC S CPUNR CPU CMD 1/3 > > > > 17450 - root root 1 9.96s 0.00s 0K 0K 0K 0K -- - R 2 100% kworker/u8:5 > > > > 4746 - martin martin 2 0.06s 0.15s 0K 0K 0K 0K -- - S 1 2% konsole > > > > 10508 - root root 1 0.13s 0.00s 0K 0K 96K 4048K -- - S 1 1% kworker/u8:18 > > > > 1488 - root root 1 0.06s 0.06s 0K 0K 0K 0K -- - S 0 1% Xorg > > > > 17332 - root root 1 0.12s 0.00s 0K 0K 96K 580K -- - R 3 1% kworker/u8:4 > > > > 17454 - root root 1 0.11s 0.00s 0K 0K 32K 4416K -- - D 1 1% kworker/u8:6 > > > > 17516 - root root 1 0.09s 0.00s 0K 0K 16K 136K -- - S 3 1% kworker/u8:7 > > > > 3268 - martin martin 3 0.02s 0.05s 0K 0K 0K 0K -- - S 1 1% kwin > > > > 10036 - root root 1 0.05s 0.02s 0K 0K 0K 0K -- - R 0 1% atop > > > > > > > > > > > > > > > > So BTRFS is basically busy with itself and nothing else. Look at the SSD > > > > usage. They are *idling* around. Heck 2400 write accesses in 10 seconds. > > > > Thats a joke with SSDs that can do 40000 IOPS (depending on how and what > > > > you measure of course, like request size, read, write, iodepth and so). > > > > > > > > Its kworker/u8:5 utilizing 100% of one core for minutes. > > > > > > > > > > > > > > > > Its the random write case it seems. Here are values from fio job: > > > > > > > > martin@merkaba:~> fio ssd-test.fio > > > > seq-write: (g=0): rw=write, bs=4K-4K/4K-4K/4K-4K, ioengine=sync, iodepth=1 > > > > rand-write: (g=1): rw=randwrite, bs=4K-4K/4K-4K/4K-4K, ioengine=sync, iodepth=1 > > > > fio-2.1.11 > > > > Starting 2 processes > > > > Jobs: 1 (f=1): [_(1),w(1)] [3.6% done] [0KB/0KB/0KB /s] [0/0/0 iops] [eta 01h:06m:26s] > > > > seq-write: (groupid=0, jobs=1): err= 0: pid=19212: Sat Dec 27 13:48:33 2014 > > > > write: io=4096.0MB, bw=343683KB/s, iops=85920, runt= 12204msec > > > > clat (usec): min=3, max=38048, avg=10.52, stdev=205.25 > > > > lat (usec): min=3, max=38048, avg=10.66, stdev=205.43 > > > > clat percentiles (usec): > > > > | 1.00th=[ 4], 5.00th=[ 4], 10.00th=[ 4], 20.00th=[ 4], > > > > | 30.00th=[ 4], 40.00th=[ 5], 50.00th=[ 5], 60.00th=[ 5], > > > > | 70.00th=[ 7], 80.00th=[ 8], 90.00th=[ 8], 95.00th=[ 9], > > > > | 99.00th=[ 14], 99.50th=[ 20], 99.90th=[ 211], 99.95th=[ 2128], > > > > | 99.99th=[10304] > > > > bw (KB /s): min=164328, max=812984, per=100.00%, avg=345585.75, stdev=201695.20 > > > > lat (usec) : 4=0.18%, 10=95.31%, 20=4.00%, 50=0.18%, 100=0.12% > > > > lat (usec) : 250=0.12%, 500=0.02%, 750=0.01%, 1000=0.01% > > > > lat (msec) : 2=0.01%, 4=0.01%, 10=0.03%, 20=0.01%, 50=0.01% > > > > cpu : usr=13.55%, sys=46.89%, ctx=7810, majf=0, minf=6 > > > > IO depths : 1=100.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0% > > > > submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0% > > > > complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0% > > > > issued : total=r=0/w=1048576/d=0, short=r=0/w=0/d=0 > > > > latency : target=0, window=0, percentile=100.00%, depth=1 > > > > > > > > Seems fine. > > > > > > > > > > > > But: > > > > > > > > rand-write: (groupid=1, jobs=1): err= 0: pid=19243: Sat Dec 27 13:48:33 2014 > > > > write: io=140336KB, bw=1018.4KB/s, iops=254, runt=137803msec > > > > clat (usec): min=4, max=21299K, avg=3708.02, stdev=266885.61 > > > > lat (usec): min=4, max=21299K, avg=3708.14, stdev=266885.61 > > > > clat percentiles (usec): > > > > | 1.00th=[ 4], 5.00th=[ 5], 10.00th=[ 5], 20.00th=[ 5], > > > > | 30.00th=[ 6], 40.00th=[ 6], 50.00th=[ 6], 60.00th=[ 6], > > > > | 70.00th=[ 7], 80.00th=[ 7], 90.00th=[ 9], 95.00th=[ 10], > > > > | 99.00th=[ 18], 99.50th=[ 19], 99.90th=[ 28], 99.95th=[ 116], > > > > | 99.99th=[16711680] > > > > bw (KB /s): min= 0, max= 3426, per=100.00%, avg=1030.10, stdev=938.02 > > > > lat (usec) : 10=92.63%, 20=6.89%, 50=0.43%, 100=0.01%, 250=0.02% > > > > lat (msec) : 250=0.01%, 500=0.01%, >=2000=0.02% > > > > cpu : usr=0.06%, sys=1.59%, ctx=28720, majf=0, minf=7 > > > > IO depths : 1=100.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0% > > > > submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0% > > > > complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0% > > > > issued : total=r=0/w=35084/d=0, short=r=0/w=0/d=0 > > > > latency : target=0, window=0, percentile=100.00%, depth=1 > > > > > > > > Run status group 0 (all jobs): > > > > WRITE: io=4096.0MB, aggrb=343682KB/s, minb=343682KB/s, maxb=343682KB/s, mint=12204msec, maxt=12204msec > > > > > > > > Run status group 1 (all jobs): > > > > WRITE: io=140336KB, aggrb=1018KB/s, minb=1018KB/s, maxb=1018KB/s, mint=137803msec, maxt=137803msec > > > > > > > > > > > > What? 254 IOPS? With a Dual SSD BTRFS RAID 1? > > > > > > > > What? > > > > > > > > Ey, *what*? > > […] > > > > There we go: > > > > > > > > Bug 90401 - btrfs kworker thread uses up 100% of a Sandybridge core for minutes on random write into big file > > > > https://bugzilla.kernel.org/show_bug.cgi?id=90401 > > > > > > I have done more tests. > > > > > > This is on the same /home after extending it to 170 GiB and balancing it to > > > btrfs balance start -dusage=80 > > > > > > It has plenty of free space free. I updated the bug report and hope it can > > > give an easy enough to comprehend summary. The new tests are in: > > > > > > https://bugzilla.kernel.org/show_bug.cgi?id=90401#c6 > > > > > > > > > > > > Pasting below for discussion on list. Summary: I easily get 38000 (!) > > > IOPS. It may be an idea to reduce to 160 GiB, but right now this does > > > not work as it says no free space on device when trying to downsize it. > > > I may try with 165 or 162GiB. > > > > > > So now we have three IOPS figures: > > > > > > - 256 IOPS in worst case scenario > > > - 4700 IOPS when trying to reproduce worst case scenario with a fresh and small > > > BTRFS > > > - 38000 IOPS when /home has unused device space to allocate chunks from > > > > > > https://bugzilla.kernel.org/show_bug.cgi?id=90401#c8 > > > > > > > > > This is another test. > > > > > > Okay, and this is the last series of tests for today. > > > > Conclusion: > > > > I cannot manage to get it down to the knees as before, but I come near to it. > > > > Still its 8000 IOPS, instead of 250 IOPS, in an according to btrfs fi sh > > even *worse* situation than before. > > > > That hints me at the need to look at the free space fragmentation, as in the > > beginning the problem started appearing with: > > > > merkaba:~> btrfs fi sh /home > > Label: 'home' uuid: […] > > Total devices 2 FS bytes used 144.41GiB > > devid 1 size 160.00GiB used 160.00GiB path /dev/mapper/msata-home > > devid 2 size 160.00GiB used 160.00GiB path /dev/mapper/sata-home > > > > Btrfs v3.17 > > merkaba:~> btrfs fi df /home > > Data, RAID1: total=154.97GiB, used=141.12GiB > > System, RAID1: total=32.00MiB, used=48.00KiB > > Metadata, RAID1: total=5.00GiB, used=3.29GiB > > GlobalReserve, single: total=512.00MiB, used=0.00B > > > > > > > > Yes, thats 13 GiB of free space *within* the chunks. > > > > So while I can get it down in IOPS by bringing it to a situation where it > > can not reserve additional data chunks again, I cannot recreate the > > abysmal 250 IOPS figure by this. Not even with my /home filesystem. > > > > So there is more to it. I think its important to look into free space > > fragmentation. It seems it needs an *aged* filesystem to recreate. At > > it seems the balances really helped. As I am not able to recreate the > > issue to that extent right now. > > > > So this shows my original idea about free device space to allocate from > > also doesn´t explain it fully. It seems to be something thats going on > > within the chunks that explains the worst case <300 IOPS, kworker using > > one core for minutes and desktop locked scenario. > > > > Is there a way to view free space fragmentation in BTRFS? > > So to rephrase that: > > From what I perceive the worst case issue happens when > > 1) BTRFS cannot reserve any new chunks from unused device space anymore. > > 2) The free space in the existing chunks is highly fragmented. > > Only one of those conditions is not sufficient to trigger it. > > Thats at least my current idea about it. With merkaba:~> btrfs fi df /home Data, RAID1: total=163.87GiB, used=146.92GiB System, RAID1: total=32.00MiB, used=48.00KiB Metadata, RAID1: total=5.94GiB, used=3.26GiB GlobalReserve, single: total=512.00MiB, used=0.00B merkaba:~> btrfs fi sh /home Label: 'home' uuid: […] Total devices 2 FS bytes used 150.18GiB devid 1 size 170.00GiB used 169.84GiB path /dev/mapper/msata-home devid 2 size 170.00GiB used 169.84GiB path /dev/mapper/sata-home Btrfs v3.17 I had a noticable hang during sdelete.exe -z in Windows XP VM with 20 GiB VDI file – Patrik on mailing list told me they have changed the argument from -c to -z as I wondered by VBoxManage modifyhd Winlala.vdi --compact did not reduce the size of the file). It was not as bad, but desktop was locked for more than 5 seconds easily. So this also happens with larger free space *within* the chunks. Before I to the VBoxManage --compact I will now rebalance partly. So this definately shows, it can happen when BTRFS cannot reserve any new chunks anymore, yet still has *plenty* of free space within the existing data chunks. -- Martin 'Helios' Steigerwald - http://www.Lichtvoll.de GPG: 03B0 0D6C 0040 0710 4AFA B82F 991B EAAC A599 84C7
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