Re: periodic daily takes a very long time to run (14-stable)
Date: Fri, 27 Oct 2023 15:23:49 UTC
Van: void <void@f-m.fm>
Datum: vrijdag, 27 oktober 2023 16:42
Aan: freebsd-stable@freebsd.org
Onderwerp: Re: periodic daily takes a very long time to run (14-stable)
>
> On Fri, Oct 27, 2023 at 03:34:35PM +0200, Ronald Klop wrote:
> >
> >What stands out to me is that you do quite a lot of writes on the disk. (I might be mistaken.)
> >The max. number of IOPS for HDD is around 80 for consumer grade harddisks. I think this counts for USB connected disks.
> >https://en.wikipedia.org/wiki/IOPS#Mechanical_hard_drives
> >From the stats you posted it looks like you are almost always doing 50+ writes/second already. That does not leave much IOPS for the find process.
> >
> >ZFS tries to bundle the writes every 5 seconds to leave room for the reads. See "sysctl vfs.zfs.txg.timeout". Unless it has too much data to write or a sync request comes in.
>
> % sysctl vfs.zfs.txg.timeout
> vfs.zfs.txg.timeout: 5
>
> do I need to tune this?
>
> Here's equivalent output from my setup (I ran periodic daily again)
>
> #device r/s w/s kr/s kw/s ms/r ms/w ms/o ms/t qlen %b
> da0 16 18 191.9 557.9 50 8 144 29 10 24 da0 107 0 699.7 0.0 52 0 0 52 1 99 da0 102 0 409.2 0.0 71 0 0 71 2 98 da0 65 6 259.6 49.4 101 143 0 105 12 101 da0 57 14 227.7 123.9 153 163 0 155 12 100 da0 40 19 158.8 285.8 205 103 0 172 12 98 da0 46 30 191.1 441.9 180 58 0 132 11 91 da0 63 4 261.6 16.1 162 250 239 170 6 112 da0 67 10 273.7 83.6 99 66 0 95 12 91 da0 32 21 129.4 177.9 223 102 0 175 5 97 da0 48 16 191.9 261.3 173 130 0 162 9 109 da0 38 19 152.2 191.3 168 61 292 139 8 104 da0 92 0 366.9 0.0 104 0 0 104 4 100 da0 73 10 291.7 87.9 76 99 0 79 12 97 da0 49 15 195.2 270.9 156 129 0 150 11 103 da0 53 15 212.3 248.3 139 128 0 137 12 92 da0 54 22 216.1 272.1 151 81 92 130 8 107 da0 80 4 320.9 16.0 74 201 125 80 3 100 da0 55 10 218.8 72.9 89 73 0 87 11 82 ^C
>
> % zpool iostat 1
> capacity operations bandwidth
> pool alloc free read write read write
> ---------- ----- ----- ----- ----- ----- -----
> zroot 93.6G 818G 13 16 161K 506K
> zroot 93.6G 818G 91 0 367K 0
> zroot 93.6G 818G 113 0 454K 0
> zroot 93.6G 818G 102 0 411K 0
> zroot 93.6G 818G 98 0 422K 0
> zroot 93.6G 818G 67 18 271K 171K
> zroot 93.6G 818G 43 16 173K 252K
> zroot 93.6G 818G 43 28 173K 376K
> zroot 93.6G 818G 78 3 315K 15.9K
> zroot 93.6G 818G 94 0 378K 0
> zroot 93.6G 818G 103 0 414K 0
> zroot 93.6G 818G 102 0 658K 0
> zroot 93.6G 818G 98 0 396K 0
> zroot 93.6G 818G 109 0 438K 0
> zroot 93.6G 818G 101 0 404K 0
> zroot 93.6G 818G 47 13 191K 91.4K
> zroot 93.6G 818G 52 11 209K 126K
> zroot 93.6G 818G 50 20 202K 301K
> zroot 93.6G 818G 46 12 186K 128K
> zroot 93.6G 818G 86 0 346K 3.93K
> zroot 93.6G 818G 45 18 183K 172K
> zroot 93.6G 818G 42 15 172K 343K
> zroot 93.6G 818G 43 24 173K 211K
> zroot 93.6G 818G 87 0 596K 0
> ^C
>
> >So if my observation is right it might be interesting to find out what is writing.
> would ktrace and/or truss be useful? something else? The truss -p output of the
> find PID produces massive amounts of output, all like this:
>
> fstatat(AT_FDCWD,"5e70d5f895ccc92af6a7d5226f818b-81464.o",{ mode=-rw-r--r-- ,inode=367004,size=10312,blksize=10752 },AT_SYMLINK_NOFOLLOW) = 0 (0x0)
>
> with the filename changing each time
>
> (later...)
>
> that file is in ccache!!!
>
> locate 5e70d5f895ccc92af6a7d5226f818b-81464.o
> /var/cache/ccache/f/5/5e70d5f895ccc92af6a7d5226f818b-81464.o
>
> maybe if I can exclude that dir (and /usr/obj) it'll lessen the periodic runtime.
> But i don't know yet whats calling find(1) when periodic daily runs. If I can, I might be able to tell it not to walk certain heirarchies.
>
> >I had similar issues after the number of jails on my RPI4 increased and they all >were doing a little bit of writing which accumulated in quite a lot of writing.
>
> I'm at a loss as to what's doing the writing. The system runs the following:
>
> poudriere-devel # for aarch64 and armv7
> apcupsd # for ups monitoring
> vnstat # bandwidth use, writes to its db in /var/db/vnstat
> sshd
> exim (local)
> pflogd # right now it's behind a firewall, on NAT so it's not doing much
> pf # same
> ntpd
> powerd
> nginx # this serves the poudriere web frontend, and that's it (http-only) syslogd
>
> >My solution was to add an SSD.
>
> I have an nfs alternative. The LAN is 1GB. But I think the fix will be to tell find
> to not search some paths. just need to work out how to do it.
>
> What would the effect be of increasing or decreasing the txg delta with system
> performance?
> --
> >
>
>
>
>
Well. You could remove daily_clean_disks_enable="YES" from /etc/periodic.conf. That saves you the "find". I have never used it before. The default is "off".
$ grep clean_disks /etc/defaults/periodic.conf
daily_clean_disks_enable="NO" # Delete files daily
daily_clean_disks_files="[#,]* .#* a.out *.core *.CKP .emacs_[0-9]*"
daily_clean_disks_days=3 # If older than this
The list of files it checks for doesn't look very useful to me in 2023. This does do a full find over *all* directories and files. *every day* ???
If you have a lot of *.core files you are better of putting this in sysctl.conf: kern.corefile=/var/tmp/%U.%N.%I.%P.core . So you know where to look to delete them.
Actually my RPI3 has this in cron: @daily find /var/tmp/ -name "*.core" -mtime +7 -ls -delete .
About the vfs.zfs.txg.timeout. Don't mess with it if you don't have a solid reason. It used to be 30 seconds when ZFS was new if I remember correctly. But it could give too big write bursts which paused the system noticeably. This is all from memory. I might be totally wrong here. :-)
The stats of your system look pretty reasonable. Also the zpool iostat 1 indicates periods of no writes. So that is ok. You just have a lot of IOPS for 1 spinning disk when everything runs together. Poudriere & ccache indicate that you are using it for compiling pkgs or other stuff. That is pretty heavy for you setup if you manage to run things in parallel as the RPI4 has 4CPUs. It doesn't help to run daily_cleanup together. ;-)
Regards,
Ronald.