linux-kernel - Re: [RFC] mm/compaction: ignore block suitable after check large free page

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Date:   Fri, 10 Mar 2017 17:53:58 +0800
From:   Yisheng Xie <xieyisheng1@...wei.com>
To:     Vlastimil Babka <vbabka@...e.cz>, <akpm@...ux-foundation.org>,
        <mhocko@...e.com>, <mgorman@...hsingularity.net>,
        <iamjoonsoo.kim@....com>, <rientjes@...gle.com>,
        <minchan@...nel.org>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <guohanjun@...wei.com>, <qiuxishi@...wei.com>, <liubo95@...wei.com>
Subject: Re: [RFC] mm/compaction: ignore block suitable after check large free
 page

Hi Vlastimil,

Thanks for comment.
On 2017/3/10 15:30, Vlastimil Babka wrote:
> On 03/10/2017 05:20 AM, Yisheng Xie wrote:
>> If the migrate target is a large free page and we ignore suitable,
>> it may not good for defrag. So move the ignore block suitable after
>> check large free page.
> 
> Right. But in practice I expect close to no impact, because direct
> compaction shouldn't have to be called if there's a >=pageblock_order
> page already available.
> 
Maybe you are right and this change is just based on logical analyses.

Presently, only in direct compaction, we increase the compaction priority,
and ignore suitable at MIN_COMPACT_PRIORITY. I have a silly question, can
we do the similar thing in kcompactd? maybe by doing most work in kcompactd,
we can get better perf of slow path.

Thanks
Yisheng Xie

>> Signed-off-by: Yisheng Xie <xieyisheng1@...wei.com>
>> ---
>>  mm/compaction.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/mm/compaction.c b/mm/compaction.c
>> index 0fdfde0..4bf2a5d 100644
>> --- a/mm/compaction.c
>> +++ b/mm/compaction.c
>> @@ -991,9 +991,6 @@ static bool too_many_isolated(struct zone *zone)
>>  static bool suitable_migration_target(struct compact_control *cc,
>>  							struct page *page)
>>  {
>> -	if (cc->ignore_block_suitable)
>> -		return true;
>> -
>>  	/* If the page is a large free page, then disallow migration */
>>  	if (PageBuddy(page)) {
>>  		/*
>> @@ -1005,6 +1002,9 @@ static bool suitable_migration_target(struct compact_control *cc,
>>  			return false;
>>  	}
>>  
>> +	if (cc->ignore_block_suitable)
>> +		return true;
>> +
>>  	/* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
>>  	if (migrate_async_suitable(get_pageblock_migratetype(page)))
>>  		return true;
>>
> 
> 
> .
>