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

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Date:   Wed, 7 Jun 2017 11:07:22 +0800
From:   zhong jiang <zhongjiang@...wei.com>
To:     Minchan Kim <minchan@...nel.org>
CC:     vinayak menon <vinayakm.list@...il.com>,
        Vinayak Menon <vinmenon@...eaurora.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        <mgorman@...hsingularity.net>, <vbabka@...e.cz>, <mhocko@...e.com>,
        Rik van Riel <riel@...hat.com>, <vdavydov.dev@...il.com>,
        <anton.vorontsov@...aro.org>,
        Shiraz Hashim <shiraz.hashim@...il.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: vmscan: do not pass reclaimed slab to vmpressure

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