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

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Date:   Fri, 10 Mar 2017 08:30:00 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Yisheng Xie <xieyisheng1@...wei.com>, 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

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.

> 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;
>