Re: [RFC] writeback and cgroup

[Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

Hey, Vivek.

On Wed, Apr 04, 2012 at 04:18:16PM -0400, Vivek Goyal wrote:
> Hey how about reconsidering my other proposal for which I had posted
> the patches. And that is keep throttling still at device level. Reads
> and direct IO get throttled asynchronously but buffered writes get
> throttled synchronously.
> 
> Advantages of this scheme.
> 
> - There are no separate knobs.
> 
> - All the IO (read, direct IO and buffered write) is controlled using
>   same set of knobs and goes in queue of same cgroup.
> 
> - Writeback logic has no knowledge of throttling. It just invokes a 
>   hook into throttling logic of device queue.
> 
> I guess this is a hybrid of active writeback throttling and back pressure
> mechanism.
> 
> But it still does not solve the NFS issue as well as for direct IO,
> filesystems still can get serialized, so metadata issue still needs to 
> be resolved. So one can argue that why not go for full "back pressure"
> method, despite it being more complex.
> 
> Here is the link, just to refresh the memory. Something to keep in mind
> while assessing alternatives.
> 
> https://lkml.org/lkml/2011/6/28/243

Hmmm... so, this only works for blk-throttle and not with the weight.
How do you manage interaction between buffered writes and direct
writes for the same cgroup?

Thanks.

-- 
tejun