Re: [PATCH] mm: vmscan: do not pass reclaimed slab to vmpressure

From: zhong jiang <zhongjiang@huawei.com>
To: Minchan Kim <minchan@kernel.org>
Cc: vinayak menon <vinayakm.list@gmail.com>,
	Vinayak Menon <vinmenon@codeaurora.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	mgorman@techsingularity.net, vbabka@suse.cz, mhocko@suse.com,
	Rik van Riel <riel@redhat.com>,
	vdavydov.dev@gmail.com, anton.vorontsov@linaro.org,
	Shiraz Hashim <shiraz.hashim@gmail.com>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: vmscan: do not pass reclaimed slab to vmpressure
Date: Wed, 7 Jun 2017 11:07:22 +0800	[thread overview]
Message-ID: <59376DEA.2080900@huawei.com> (raw)
In-Reply-To: <20170607025324.GB18007@bbox>

On 2017/6/7 10:53, Minchan Kim wrote:
> Hi,
>
> On Tue, Jun 06, 2017 at 09:00:55PM +0800, zhong jiang wrote:
>> On 2017/1/31 7:40, Minchan Kim wrote:
>>> Hi Vinayak,
>>> Sorry for late response. It was Lunar New Year holidays.
>>>
>>> On Fri, Jan 27, 2017 at 01:43:23PM +0530, vinayak menon wrote:
>>>>> Thanks for the explain. However, such case can happen with THP page
>>>>> as well as slab. In case of THP page, nr_scanned is 1 but nr_reclaimed
>>>>> could be 512 so I think vmpressure should have a logic to prevent undeflow
>>>>> regardless of slab shrinking.
>>>>>
>>>> I see. Going to send a vmpressure fix. But, wouldn't the THP case
>>>> result in incorrect
>>>> vmpressure reporting even if we fix the vmpressure underflow problem ?
>>> If a THP page is reclaimed, it reports lower pressure due to bigger
>>> reclaim ratio(ie, reclaimed/scanned) compared to normal pages but
>>> it's not a problem, is it? Because VM reclaimed more memory than
>>> expected so memory pressure isn't severe now.
>>   Hi, Minchan
>>
>>   THP lru page is reclaimed, reclaim ratio bigger make sense. but I read the code, I found
>>   THP is split to normal pages and loop again.  reclaimed pages should not be bigger
>>    than nr_scan.  because of each loop will increase nr_scan counter.
>>  
>>    It is likely  I miss something.  you can point out the point please.
> You are absolutely right.
>
> I got confused by nr_scanned from isolate_lru_pages and sc->nr_scanned
> from shrink_page_list.
>
> Thanks.
>
>
> .
>
 Hi, Minchan

 I will send the revert patch shortly. how do you think?

 Thanks
 zhongjiang

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