linux-kernel - Re: [PATCH v3 01/10] compaction: trivial clean up acct

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Date:	Thu, 9 Jun 2011 14:33:27 +0100
From:	Mel Gorman <mgorman@...e.de>
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>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH v3 01/10] compaction: trivial clean up acct_isolated

On Tue, Jun 07, 2011 at 11:38:14PM +0900, Minchan Kim wrote:
> acct_isolated of compaction uses page_lru_base_type which returns only
> base type of LRU list so it never returns LRU_ACTIVE_ANON or LRU_ACTIVE_FILE.
> In addtion, cc->nr_[anon|file] is used in only acct_isolated so it doesn't have
> fields in conpact_control.
> This patch removes fields from compact_control and makes clear function of
> acct_issolated which counts the number of anon|file pages isolated.
> 
> Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Andrea Arcangeli <aarcange@...hat.com>
> Acked-by: Rik van Riel <riel@...hat.com>
> Acked-by: Johannes Weiner <hannes@...xchg.org>
> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Signed-off-by: Minchan Kim <minchan.kim@...il.com>
> ---
>  mm/compaction.c |   18 +++++-------------
>  1 files changed, 5 insertions(+), 13 deletions(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 021a296..61eab88 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -35,10 +35,6 @@ struct compact_control {
>  	unsigned long migrate_pfn;	/* isolate_migratepages search base */
>  	bool sync;			/* Synchronous migration */
>  
> -	/* Account for isolated anon and file pages */
> -	unsigned long nr_anon;
> -	unsigned long nr_file;
> -
>  	unsigned int order;		/* order a direct compactor needs */
>  	int migratetype;		/* MOVABLE, RECLAIMABLE etc */
>  	struct zone *zone;
> @@ -212,17 +208,13 @@ static void isolate_freepages(struct zone *zone,
>  static void acct_isolated(struct zone *zone, struct compact_control *cc)
>  {
>  	struct page *page;
> -	unsigned int count[NR_LRU_LISTS] = { 0, };
> +	unsigned int count[2] = { 0, };
>  
> -	list_for_each_entry(page, &cc->migratepages, lru) {
> -		int lru = page_lru_base_type(page);
> -		count[lru]++;
> -	}
> +	list_for_each_entry(page, &cc->migratepages, lru)
> +		count[!!page_is_file_cache(page)]++;
>  
> -	cc->nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON];
> -	cc->nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];
> -	__mod_zone_page_state(zone, NR_ISOLATED_ANON, cc->nr_anon);
> -	__mod_zone_page_state(zone, NR_ISOLATED_FILE, cc->nr_file);
> +	__mod_zone_page_state(zone, NR_ISOLATED_ANON, count[0]);
> +	__mod_zone_page_state(zone, NR_ISOLATED_FILE, count[1]);

You are hard-coding assumptions about the value of LRU_INACTIVE_ANON
and LRU_INACTIVE_FILE here. I have no expectation that these will
change but who knows for sure? To be robust against unexpected
changes, count should still be NR_LRU_LISTS and you should use the
LRU_INACTIVE_ANON and LRU_INACTIVE_FILE values.

I agree that summing LRU_ACTIVE_* is silly.

-- 
Mel Gorman
SUSE Labs
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