Re: kswapd CPU usage and heavy disk IO

Dieter Nützel (Dieter.Nuetzel@hamburg.de)
Thu, 9 Jan 2003 17:42:51 +0100

Am Donnerstag, 9. Januar 2003 17:02 schrieb Brian Tinsley:
> I've been seeing the exact same thing on the same type of system in the
> same situations. This has been causing all kinds of problems on our
> clusters: the system live-locks for a minute or two, causes cluster
> heartbeats to not be received, and falsely fails over when the system
> recovers from the live-lock. The only thing I can find after the
> live-lock is that the runtime for kswapd is abnormally high.
>
> We started running sar (60 second collection interval) and were able to
> capture some stats during this live-lock period. I've snipped some I
> believe may be of interest. Note the missing stats between 03:59:43 and
> 04:02:03
>
> Oh BTW, this is on a stock 2.4.20 kernel (dual P3, 4GB), but I have seen
> the same behavior on 2.4.19 and 2.4.17.

I think you should have cc'ed Andrea Arcangeli <andrea@suse.de>, LKM and try
2.4.20-aa1.

Are you sure it is a ReiserFS and not a kernel thing?

Regards,
Dieter

> 1. sar -f sa09 -r
>
> 03:53:43 AM kbmemfree kbmemused %memused kbmemshrd kbbuffers kbcached
> kbswpfree kbswpused %swpused
> 03:54:43 AM 411888 3888264 90.42 0 629520
> 2666968 209713
> 6 0 0.00
> 03:55:43 AM 396684 3903468 90.78 0 658656
> 2667160 209713
> 6 0 0.00
> 03:56:43 AM 331360 3968792 92.29 0 675008
> 2733476 209713
> 6 0 0.00
> 03:57:43 AM 231588 4068564 94.61 0 683680
> 2832816 209713
> 6 0 0.00
> 03:58:43 AM 209740 4090412 95.12 0 702148
> 2854332 209713
> 6 0 0.00
> 03:59:43 AM 211016 4089136 95.09 0 712580
> 2854508 209713
> 6 0 0.00
> 04:02:03 AM 207828 4092324 95.17 0 715180
> 2854596 209713
> 6 0 0.00
> 04:04:30 AM 2581956 1718196 39.96 0 662320
> 874536 209713
> 6 0 0.00
> 04:05:30 AM 4013000 287152 6.68 0 27012
> 84084 209713
> 6 0 0.00
>
> 2. sar -f sa09 -R
>
> 03:53:43 AM frmpg/s shmpg/s bufpg/s campg/s
> 03:54:43 AM -263.02 0.00 91.67 299.50
> 03:55:43 AM -63.35 0.00 121.40 0.80
> 03:56:43 AM -272.18 0.00 68.13 276.32
> 03:57:43 AM -415.72 0.00 36.13 413.92
> 03:58:43 AM -91.03 0.00 76.95 89.65
> 03:59:43 AM 5.32 0.00 43.47 0.73
> 04:02:03 AM -4.74 0.00 3.86 0.13
> 04:04:30 AM 5013.36 0.00 -111.62 -4181.22
> 04:05:30 AM 5962.68 0.00 -2647.12 -3293.55
> 04:06:30 AM -8.10 0.00 0.02 6.50
>
> 3. sar -f sa09 -b
>
> 03:53:43 AM tps rtps wtps bread/s bwrtn/s
> 03:54:43 AM 161.52 156.32 5.20 3156.67 119.60
> 03:55:43 AM 148.37 129.35 19.02 1034.80 377.33
> 03:56:43 AM 146.32 128.48 17.83 2732.80 360.40
> 03:57:43 AM 107.32 84.62 22.70 3743.60 447.07
> 03:58:43 AM 91.73 82.03 9.70 1312.40 194.80
> 03:59:43 AM 75.62 54.22 21.40 433.73 350.00
> 04:02:03 AM 4.97 4.83 0.14 38.65 1.24
> 04:04:30 AM 82.68 9.44 73.24 78.45 958.39
> 04:05:30 AM 2.93 0.00 2.93 0.00 29.33
> 04:06:30 AM 0.22 0.00 0.22 0.00 1.73
>
> 4. sar -f sa09 -i
>
> 03:53:43 AM dentunusd file-sz %file-sz inode-sz super-sz %super-sz
> dquot-sz %dquot-sz rtsig-sz %rtsig-sz
> 03:54:43 AM 57361 134 0.01 61318 0 0.00
> 0 0.00 0 0.00
> 03:55:43 AM 58318 124 0.01 62006 0 0.00
> 0 0.00 0 0.00
> 03:56:43 AM 44384 135 0.01 47145 0 0.00
> 0 0.00 0 0.00
> 03:57:43 AM 42565 135 0.01 45983 0 0.00
> 0 0.00 0 0.00
> 03:58:43 AM 18901 134 0.01 22408 0 0.00
> 0 0.00 0 0.00
> 03:59:43 AM 607 135 0.01 1173 0 0.00
> 0 0.00 0 0.00
> 04:02:03 AM 4294967295 113 0.01 417 0
> 0.00 0 0.00 4 0.39
> 04:04:30 AM 49 247 0.02 6316 0 0.00
> 0 0.00 0 0.00
> 04:05:30 AM 121 311 0.03 365 0 0.00
> 0 0.00 0 0.00
>
> 5. sar -f sa09 -u
>
> 03:53:43 AM CPU %user %nice %system %idle
> 03:54:43 AM all 7.52 0.00 25.15 67.33
> 03:55:43 AM all 8.97 0.00 25.28 65.75
> 03:56:43 AM all 6.07 0.00 23.82 70.11
> 03:57:43 AM all 5.08 0.00 23.54 71.38
> 03:58:43 AM all 6.77 0.00 22.88 70.36
> 03:59:43 AM all 7.18 0.00 25.82 67.00
> 04:02:03 AM all 0.77 0.00 96.32 2.91
> 04:04:30 AM all 4.20 0.00 95.11 0.69
> 04:05:30 AM all 1.88 0.00 5.29 92.83
> 04:06:30 AM all 2.01 0.00 2.81 95.18
>
> Russell Coker wrote:
> >I have a server with 4G of RAM running ReiserFS for everything that
> > matters.
> >
> >It has 2G of swap space free, but so far I have not seen swap usage go
> > above 1.6M (so in normal use I could turn off swap entirely and expect
> > not to see much difference).
> >
> >When it's under really heavy load (when I have a maintenance task
> > involving a "find /" and there are lots of POP/IMAP clients hitting the
> > server as well as mail delivery) and the load average gets to about 40,
> > the "kswapd" kernel thread starts using excessive CPU time. It will stay
> > on ~4% but have spikes of up to 45%!!! This is a two-processor machine
> > so 45% CPU reported by top means 90% of a single CPU I guess. 90% of a
> > 1.8GHz P4 CPU is a lot of CPU and I think that something is wrong.
> >
> >In the meager documentation in the kernel source kswapd is described as
> > being involved in paging to disk. I don't think that this is what it is
> > doing as there is no noticable paging activity (it generally has at least
> > 600M of "buffers" so there is no real shortage of memory).
> >
> >Would the activity of kswapd be involved with ReiserFS in any way? What
> > can I do to improve this situation?

-- 
Dieter Nützel
Graduate Student, Computer Science


University of Hamburg
Department of Computer Science
@home: Dieter.Nuetzel at hamburg.de (replace at with @)


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