linux-kernel - Re: [RFC 8/8] compaction: make compaction use in-order putback

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Date:	Wed, 27 Apr 2011 17:39:22 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Christoph Lameter <cl@...ux.com>,
	Johannes Weiner <jweiner@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [RFC 8/8] compaction: make compaction use in-order putback

On Wed, 27 Apr 2011 01:25:25 +0900
Minchan Kim <minchan.kim@...il.com> wrote:

> Compaction is good solution to get contiguos page but it makes
> LRU churing which is not good.
> This patch makes that compaction code use in-order putback so
> after compaction completion, migrated pages are keeping LRU ordering.
> 
> Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Rik van Riel <riel@...hat.com>
> Cc: Andrea Arcangeli <aarcange@...hat.com>
> Signed-off-by: Minchan Kim <minchan.kim@...il.com>
> ---
>  mm/compaction.c |   22 +++++++++++++++-------
>  1 files changed, 15 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index a2f6e96..480d2ac 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -211,11 +211,11 @@ static void isolate_freepages(struct zone *zone,
>  /* Update the number of anon and file isolated pages in the zone */
>  static void acct_isolated(struct zone *zone, struct compact_control *cc)
>  {
> -	struct page *page;
> +	struct pages_lru *pages_lru;
>  	unsigned int count[NR_LRU_LISTS] = { 0, };
>  
> -	list_for_each_entry(page, &cc->migratepages, lru) {
> -		int lru = page_lru_base_type(page);
> +	list_for_each_entry(pages_lru, &cc->migratepages, lru) {
> +		int lru = page_lru_base_type(pages_lru->page);
>  		count[lru]++;
>  	}
>  
> @@ -281,6 +281,7 @@ static unsigned long isolate_migratepages(struct zone *zone,
>  	spin_lock_irq(&zone->lru_lock);
>  	for (; low_pfn < end_pfn; low_pfn++) {
>  		struct page *page;
> +		struct pages_lru *pages_lru;
>  		bool locked = true;
>  
>  		/* give a chance to irqs before checking need_resched() */
> @@ -334,10 +335,16 @@ static unsigned long isolate_migratepages(struct zone *zone,
>  			continue;
>  		}
>  
> +		pages_lru = kmalloc(sizeof(struct pages_lru), GFP_ATOMIC);
> +		if (pages_lru)
> +			continue;

Hmm, can't we use fixed size of statically allocated pages_lru, per-node or
per-zone ? I think using kmalloc() in memory reclaim path is risky.

Thanks,
-Kame

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