[ale] thoughts on reducing Sync time for 2.6.32 System?

[Phil Turmel]

On 01/21/2014 09:18 PM, Neal Rhodes wrote:
> Searching on this more, I find
> http://www.westnet.com/~gsmith/content/linux-pdflush.htm 
> 
> How is this for a working hypothesis:  
> 
> Old Dell servers were 8GB, and I think our DB buffering might have used
> 2GB of that. 
> 
> New Dell servers are 24GB, and Progress OpenEdge is 64 bit, and uses a
> good bit more buffer space. 
> 
> /proc/sys/vm/dirty_background_ratio is the same 10%, but that's 3X the
> amount of dirty accumulated. 
> 
> According to /proc/meminfo, I've seen Dirty: over 3013kB. 
> 
> It would seem that dropping /proc/sys/vm/dirty_background_ratio to 6%
> might be worth a stab to see if it evens out the peak sync times.   It's
> not that the system is slow, it's just when we bust through a 3 second
> SLA the client goes bat-crazy.

There's been discussion on lkml regularly of the past few years about
this problem, and it is as you suspect.  The most recent proposal was to
set a default dirty_background_bytes instead of _ratio.  You may want to
experiment with all of the dirty_ settings.

Phil