Messages in this thread | | | Date | Tue, 13 Nov 2012 14:51:59 +0100 | From | Jan Kara <> | Subject | Re: Debugging system freezes on filesystem writes |
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On Fri 09-11-12 15:12:43, Marcus Sundman wrote: > On 09.11.2012 01:41, Marcus Sundman wrote: > >On 07.11.2012 18:17, Jan Kara wrote: > >>On Fri 02-11-12 04:19:24, Marcus Sundman wrote: > >>>Also, and this might be important, according to iotop there is > >>>almost no disk writing going on during the freeze. (Occasionally > >>>there are a few MB/s, but mostly it's 0-200 kB/s.) Well, at least > >>>when an iotop running on nice -20 hasn't frozen completely, which it > >>>does during the more severe freezes. > >> OK, it seems as if your machine has some problems with memory > >>allocations. Can you capture /proc/vmstat before the freeze and > >>after the > >>freeze and send them for comparison. Maybe it will show us what is the > >>system doing. > > > >t=01:06 http://sundman.iki.fi/vmstat.pre-freeze.txt > >t=01:08 http://sundman.iki.fi/vmstat.during-freeze.txt > >t=01:12 http://sundman.iki.fi/vmstat.post-freeze.txt > > Here are some more vmstats: > http://sundman.iki.fi/vmstats.tar.gz > > They are from running this: > while true; do cat /proc/vmstat > "vmstat.$(date +%FT%X).txt"; sleep > 10; done > > There were lots and lots of freezes for almost 20 mins from 14:37:45 > onwards, pretty much constantly, but at 14:56:50 the freezes > suddenly stopped and everything went back to how it should be. I was looking into the data but they didn't show anything problematic. The machine seems to be writing a lot but there's always some free memory, even direct reclaim isn't ever entered. Hum, actually you wrote iotop isn't showing much IO going on but vmstats show there is about 1 GB written during the freeze. It is not a huge amount given the time span but it certainly gives a few MB/s of write load.
There's surprisingly high number of allocations going on but that may be due to the IO activity. So let's try something else: Can you switch to console and when the hang happens press Alt-Sysrq-w (or you can just do "echo w >/proc/sysrq-trigger" if the machine is live enough to do that). Then send me the output from dmesg. Thanks!
Honza -- Jan Kara <jack@suse.cz> SUSE Labs, CR
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