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

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

> > > 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)
> 
> No.
> 
> it isn't enough.
> after is does, order-1 allocation case twrice reclaim (soft limit shrinking
> and normal try_to_free_pages()).
> then, order-1 reclaim makes slower about 2 times.
> 
> unfortunately, order-1 allocation is very frequent. it is used for
> kernel stack.

in normal order-1 reclaim is:

1. try_to_free_pages()
2. get_page_from_freelist()
3. retry if order-1 page don't exist

Coundn't you use the same logic?

> > > - 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.
> 
> No.
> 
> My point is, contention case kswapd wakeup. and kswapd reclaim by
> global lru order before soft limit shrinking.
> Therefore, In typical usage, mem_cgroup_soft_limit_reclaim() almost
> don't call properly.
> 
> soft limit shrinking should run before processing global reclaim.

Do you have the reason of disliking call from kswapd ?



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