Re: Heavy I/O causing slow interactivity

[Michal Hocko <mhocko@kernel.org>]

On Wed 05-04-17 11:15:44, Raymond Jennings wrote:
> I have 32GiB of memory
> 
> Storage is an LVM volume group sitting on a pair of 2T western digital
> drives, one WD Green, and the other WD Blue
> 
> My CPU is an i7, model 4790K.
> 
> What I'd like is some way for my system to fairly share the available
> I/O bandwidth.  My youtube is sensitive to latency but doesn't chew up
> a lot of throughput.  My I/O heavy stuff isn't really urgent and I
> don't mind it yielding to the interactive stuff.
> 
> I remember a similiar concept being tried awhile ago with a scheduler
> that "punished" processes that sucked up too much CPU and made sure
> the short sporadic event driven interactive stuff got the scraps of
> CPU when it needed them.
> 
> /proc/sys/vm/dirty is set up as follows
> 
> dirty_ratio 90

So you allow 90% of your 32GB to be dirty and then get throttled which
will take quite some time until it gets synced to the disk. Even with a
fast storage. I would really recommend reducing dirty_ratio (and
background ratio as well) to something much more reasonable. E.g. start
the background IO at around 400MB and hard limit at 800MB. I am pretty
sure that the stalls you are seeing are related to the IO dirty
throttling.

-- 
Michal Hocko
SUSE Labs

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