Re: [PATCH 4/4] Memory controller soft limit reclaim on contention (v5)

[Balbir Singh <balbir@linux.vnet.ibm.com>]

* KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> [2009-03-13 10:36:31]:

> Hi
> 
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 46bd24c..b49c90f 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -1583,7 +1583,14 @@ nofail_alloc:
> >  	reclaim_state.reclaimed_slab = 0;
> >  	p->reclaim_state = &reclaim_state;
> >  
> > -	did_some_progress = try_to_free_pages(zonelist, order, gfp_mask);
> > +	/*
> > +	 * Try to free up some pages from the memory controllers soft
> > +	 * limit queue.
> > +	 */
> > +	did_some_progress = mem_cgroup_soft_limit_reclaim(zonelist, gfp_mask);
> > +	if (!order || !did_some_progress)
> > +		did_some_progress += try_to_free_pages(zonelist, order,
> > +							gfp_mask);
> 
> I have two objection to this.
> 
> - "if (!order || !did_some_progress)" mean no call try_to_free_pages()
>   in order>0 and did_some_progress>0 case.
>   but mem_cgroup_soft_limit_reclaim() don't have lumpy reclaim.
>   then, it break high order reclaim.

I am sending a fix for this right away. Thanks, the check should be
if (order || !did_some_progress)

> - in global reclaim view, foreground reclaim and background reclaim's
>   reclaim rate is about 1:9 typically.
>   then, kswapd reclaim the pages by global lru order before proceccing
>   this logic.
>   IOW, this soft limit is not SOFT.

It depends on what you mean by soft. I call them soft since they are
imposed only when there is contention. If you mean kswapd runs more
often than direct reclaim, that is true, but it does not impact this
code extensively since the high water mark is a very small compared to
the pages present on the system.

-- 
	Balbir

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