linux-kernel - Re: [PATCH] Revert "mm: vmpressure: fix sending wrong events on underflow"

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Date:   Wed, 7 Jun 2017 12:56:57 +0800
From:   zhong jiang <zhongjiang@...wei.com>
To:     Minchan Kim <minchan@...nel.org>
CC:     <akpm@...ux-foundation.org>, <vinayakm.list@...il.com>,
        <mhocko@...e.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Revert "mm: vmpressure: fix sending wrong events on underflow"

On 2017/6/7 11:55, Minchan Kim wrote:
> On Wed, Jun 07, 2017 at 11:08:37AM +0800, zhongjiang wrote:
>> This reverts commit e1587a4945408faa58d0485002c110eb2454740c.
>>
>> THP lru page is reclaimed , THP is split to normal page and loop again.
>> reclaimed pages should not be bigger than nr_scan.  because of each
>> loop will increase nr_scan counter.
> Unfortunately, there is still underflow issue caused by slab pages as
> Vinayak reported in description of e1587a4945408 so we cannot revert.
> Please correct comment instead of removing the logic.
>
> Thanks.
  we calculate the vmpressue based on the Lru page, exclude the slab pages by previous
  discussion.    is it not this?

  Thanks
 zhongjiang
>> Signed-off-by: zhongjiang <zhongjiang@...wei.com>
>> ---
>>  mm/vmpressure.c | 10 +---------
>>  1 file changed, 1 insertion(+), 9 deletions(-)
>>
>> diff --git a/mm/vmpressure.c b/mm/vmpressure.c
>> index 6063581..149fdf6 100644
>> --- a/mm/vmpressure.c
>> +++ b/mm/vmpressure.c
>> @@ -112,16 +112,9 @@ static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned,
>>  						    unsigned long reclaimed)
>>  {
>>  	unsigned long scale = scanned + reclaimed;
>> -	unsigned long pressure = 0;
>> +	unsigned long pressure;
>>  
>>  	/*
>> -	 * reclaimed can be greater than scanned in cases
>> -	 * like THP, where the scanned is 1 and reclaimed
>> -	 * could be 512
>> -	 */
>> -	if (reclaimed >= scanned)
>> -		goto out;
>> -	/*
>>  	 * We calculate the ratio (in percents) of how many pages were
>>  	 * scanned vs. reclaimed in a given time frame (window). Note that
>>  	 * time is in VM reclaimer's "ticks", i.e. number of pages
>> @@ -131,7 +124,6 @@ static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned,
>>  	pressure = scale - (reclaimed * scale / scanned);
>>  	pressure = pressure * 100 / scale;
>>  
>> -out:
>>  	pr_debug("%s: %3lu  (s: %lu  r: %lu)\n", __func__, pressure,
>>  		 scanned, reclaimed);
>>  
>> -- 
>> 1.7.12.4
>>
> .
>