Re: [PATCH 5/7] memcg bgreclaim core.

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Wed, 27 Apr 2011 09:10:30 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

> On Tue, 26 Apr 2011 16:15:04 -0700
> Ying Han <yinghan@google.com> wrote:
> > So, here we fix the amount of work per-memcg, and the performance for those
> > jobs will be hurt. If i understand
> > correctly, we only have one workitem on the workqueue per memcg. So which
> > means we can only reclaim those amount of pages for each iteration. And if
> > the queue is big, those jobs(heavy memory allocating, and willing to pay cpu
> > to do bg reclaim) will hit direct reclaim more than necessary.
> > 
> 
> But, from measurements, we cannot reclaim enough memory on time if the work
> is busy. Can you think of 'make -j 8' doesn't hit the limit by bgreclaim ?
> 
> 'Working hard' just adds more CPU consumption and results more latency.
> From my point of view, if direct reclaim has problematic costs, bgreclaim is
> not easy and slow, too. Then, 'work harder' cannot be help. And spike of
> memory consumption can be very rapid. If an application exec an application
> which does malloc(2G), under 1G limit memcg, we cannot avoid direct reclaim.
> 
> I think the user can set limit higher and distance between limit <-> wmark large.
> Then, he can gain more time and avoid hitting direct relcaim. How about enlarging
> limit <-> wmark range for performance intensive jobs ?
> Amount of work per memcg is limit <-> wmark range, I guess.
> 

BTW, in another idea, I wonder I should limit work iterms by reducing max_active
because it may burn cpu. If we need, we can have 2 workqueues of high/low priority.
high workqueue has big max_active(0?) and low workqueue has small max_active.

Thanks,
-Kame



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