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From: Michal Hocko <mhocko@kernel.org>
To: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: David Rientjes <rientjes@google.com>,
	"Li,Rongqing" <lirongqing@baidu.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"cgroups@vger.kernel.org" <cgroups@vger.kernel.org>,
	"hannes@cmpxchg.org" <hannes@cmpxchg.org>
Subject: Re: 答复: 答复: [PATCH] mm/memcontrol.c: speed up to force empty a memory cgroup
Date: Wed, 21 Mar 2018 10:59:13 +0100	[thread overview]
Message-ID: <20180321095913.GE23100@dhcp22.suse.cz> (raw)
In-Reply-To: <e265c518-968b-8669-ad22-671c781ad96e@virtuozzo.com>

On Wed 21-03-18 01:35:05, Andrey Ryabinin wrote:
> On 03/21/2018 01:15 AM, David Rientjes wrote:
> > On Wed, 21 Mar 2018, Andrey Ryabinin wrote:
> > 
> >>>>> It would probably be best to limit the 
> >>>>> nr_pages to the amount that needs to be reclaimed, though, rather than 
> >>>>> over reclaiming.
> >>>>
> >>>> How do you achieve that? The charging path is not synchornized with the
> >>>> shrinking one at all.
> >>>>
> >>>
> >>> The point is to get a better guess at how many pages, up to 
> >>> SWAP_CLUSTER_MAX, that need to be reclaimed instead of 1.
> >>>
> >>>>> If you wanted to be invasive, you could change page_counter_limit() to 
> >>>>> return the count - limit, fix up the callers that look for -EBUSY, and 
> >>>>> then use max(val, SWAP_CLUSTER_MAX) as your nr_pages.
> >>>>
> >>>> I am not sure I understand
> >>>>
> >>>
> >>> Have page_counter_limit() return the number of pages over limit, i.e. 
> >>> count - limit, since it compares the two anyway.  Fix up existing callers 
> >>> and then clamp that value to SWAP_CLUSTER_MAX in 
> >>> mem_cgroup_resize_limit().  It's a more accurate guess than either 1 or 
> >>> 1024.
> >>>
> >>
> >> JFYI, it's never 1, it's always SWAP_CLUSTER_MAX.
> >> See try_to_free_mem_cgroup_pages():
> >> ....	
> >> 	struct scan_control sc = {
> >> 		.nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
> >>
> > 
> > Is SWAP_CLUSTER_MAX the best answer if I'm lowering the limit by 1GB?
> > 
> 
> Absolutely not. I completely on your side here. 
> I've tried to fix this recently - http://lkml.kernel.org/r/20180119132544.19569-2-aryabinin@virtuozzo.com
> I guess that Andrew decided to not take my patch, because Michal wasn't
> happy about it (see mail archives if you want more details).

I was unhappy about the explanation and justification of the patch. It
is still not clear to me why try_to_free_mem_cgroup_pages with a single
target should be slower than multiple calls of this function with
smaller batches when the real reclaim is still SWAP_CLUSTER_MAX batched.

There is also a theoretical risk of over reclaim. Especially with large
targets.

-- 
Michal Hocko
SUSE Labs

  parent reply	other threads:[~2018-03-21  9:59 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-19  8:29 Li RongQing
2018-03-19  8:53 ` Michal Hocko
     [not found]   ` <2AD939572F25A448A3AE3CAEA61328C23745764B@BC-MAIL-M28.internal.baidu.com>
2018-03-19 10:37     ` 答复: " Michal Hocko
2018-03-19 10:51       ` 答复: " Li,Rongqing
2018-03-19 17:51         ` David Rientjes
2018-03-20  8:39           ` Michal Hocko
2018-03-20 20:29             ` David Rientjes
2018-03-20 22:08               ` Andrey Ryabinin
2018-03-20 22:15                 ` David Rientjes
2018-03-20 22:35                   ` Andrey Ryabinin
2018-03-20 22:45                     ` David Rientjes
2018-03-21  9:59                     ` Michal Hocko [this message]
2018-03-23  2:58         ` Li,Rongqing
2018-03-23 10:08           ` Michal Hocko
2018-03-23 12:04             ` 答复: " Li,Rongqing
2018-03-23 12:29               ` Michal Hocko
2018-03-23 10:34 ` Michal Hocko

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