[CentOS] pdflush kernel thread pops up every 10 seconds or so and video decoding grinds to a halt for 1/2 a second

Ross Walker rswwalker at gmail.com
Wed Oct 20 09:21:26 EDT 2010


On Oct 19, 2010, at 7:34 PM, Aleksey Tsalolikhin <atsaloli.tech at gmail.com> wrote:

> Still seeing the glitch every 5-20 secs after remounting with "commit=6000".
> 
> 
> On Tue, Oct 19, 2010 at 4:00 PM, Ross Walker <rswwalker at gmail.com> wrote:
>> 
>> You could also reduce the dirty interval in sysctl so it flushes sooner therefore flushes less data each time.
> 
> OK.  It's worth a shot.  Any idea what the default value is?  I'm not
> sure what value to put in here.
> I know I want to reduce it but I don't want to break my friend's system either.
> 
> http://www.mjmwired.net/kernel/Documentation/sysctl/vm.txt
>    
> 109    dirty_expire_centisecs
> 110    
> 111    This tunable is used to define when dirty data is old enough to be eligible
> 112    for writeout by the pdflush daemons.  It is expressed in 100'ths
> of a second.
> 113    Data which has been dirty in-memory for longer than this interval will be
> 114    written out next time a pdflush daemon wakes up.

There are several dirty tunables, try a 'sysctl -a | grep dirty'

Try limiting both the amount if dirty memory to hold and the number of seconds to hold it. Defaults are way too liberal and if you are processing a lot of data can both expose you to extreme data loss in a system failure and bottle neck your storage during pdflush.

-Ross



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