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SubjectRe: [PATCH][RFC] dirty balancing for cgroups
On Fri, 11 Jul 2008 14:59:26 +0900 (JST)
yamamoto@valinux.co.jp (YAMAMOTO Takashi) wrote:

> > > > - This looks simple but, could you merge this into memory resource controller ?
> > >
> > > why?
> > >
> > 3 points.
> > 1. Is this useful if used alone ?
>
> it can be. why not?
>
> > 2. memcg requires this kind of feature, basically.
> >
> > 3. I wonder I need more work to make this work well under memcg.
>
> i'm not sure if i understand these points. can you explain a bit?
>
In my understanding, dirty_ratio is for helping memory (reclaim) subsystem.

See comments in fs/page-writeback.c:: determin_dirtyable_memory()
==
/*
* Work out the current dirty-memory clamping and background writeout
* thresholds.
*
* The main aim here is to lower them aggressively if there is a lot of mapped
* memory around. To avoid stressing page reclaim with lots of unreclaimable
* pages. It is better to clamp down on writers than to start swapping, and
* performing lots of scanning.
*
* We only allow 1/2 of the currently-unmapped memory to be dirtied.
*
* We don't permit the clamping level to fall below 5% - that is getting rather
* excessive.
*
* We make sure that the background writeout level is below the adjusted
* clamping level.
==
"To avoid stressing page reclaim with lots of unreclaimable pages"

Then, I think memcg should support this for helping relcaim under memcg.

> my patch penalizes heavy-writer cgroups as task_dirty_limit does
> for heavy-writer tasks. i don't think that it's necessary to be
> tied to the memory subsystem because i merely want to group writers.
>
Hmm, maybe what I need is different from this ;)
Does not seem to be a help for memory reclaim under memcg.


Thanks,
-Kame



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