linux-kernel - Re: [PATCH 1/2] mm/page_alloc.c: use list_{first,last}_entry instead of list

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Date:	Wed, 2 Dec 2015 17:28:29 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Geliang Tang <geliangtang@....com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Mel Gorman <mgorman@...hsingularity.net>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <js1304@...il.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Alexander Duyck <alexander.h.duyck@...hat.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mm/page_alloc.c: use list_{first,last}_entry instead
 of list_entry

On Wed 02-12-15 23:12:40, Geliang Tang wrote:
> To make the intention clearer, use list_{first,last}_entry instead
> of list_entry.

I like list_{first,last}_entry that indeed helps readability, the
_or_null is less clear from the name, though. Previous check for an
empty list was easier to read, at least for me. But it seems like
this is a general pattern...

> Signed-off-by: Geliang Tang <geliangtang@....com>

Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  mm/page_alloc.c | 23 +++++++++++------------
>  1 file changed, 11 insertions(+), 12 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index d6d7c97..0d38185 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -830,7 +830,7 @@ static void free_pcppages_bulk(struct zone *zone, int count,
>  		do {
>  			int mt;	/* migratetype of the to-be-freed page */
>  
> -			page = list_entry(list->prev, struct page, lru);
> +			page = list_last_entry(list, struct page, lru);
>  			/* must delete as __free_one_page list manipulates */
>  			list_del(&page->lru);
>  
> @@ -1457,11 +1457,10 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
>  	/* Find a page of the appropriate size in the preferred list */
>  	for (current_order = order; current_order < MAX_ORDER; ++current_order) {
>  		area = &(zone->free_area[current_order]);
> -		if (list_empty(&area->free_list[migratetype]))
> -			continue;
> -
> -		page = list_entry(area->free_list[migratetype].next,
> +		page = list_first_entry_or_null(&area->free_list[migratetype],
>  							struct page, lru);
> +		if (!page)
> +			continue;
>  		list_del(&page->lru);
>  		rmv_page_order(page);
>  		area->nr_free--;
> @@ -1740,12 +1739,12 @@ static void unreserve_highatomic_pageblock(const struct alloc_context *ac)
>  		for (order = 0; order < MAX_ORDER; order++) {
>  			struct free_area *area = &(zone->free_area[order]);
>  
> -			if (list_empty(&area->free_list[MIGRATE_HIGHATOMIC]))
> +			page = list_first_entry_or_null(
> +					&area->free_list[MIGRATE_HIGHATOMIC],
> +					struct page, lru);
> +			if (!page)
>  				continue;
>  
> -			page = list_entry(area->free_list[MIGRATE_HIGHATOMIC].next,
> -						struct page, lru);
> -
>  			/*
>  			 * It should never happen but changes to locking could
>  			 * inadvertently allow a per-cpu drain to add pages
> @@ -1793,7 +1792,7 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
>  		if (fallback_mt == -1)
>  			continue;
>  
> -		page = list_entry(area->free_list[fallback_mt].next,
> +		page = list_first_entry(&area->free_list[fallback_mt],
>  						struct page, lru);
>  		if (can_steal)
>  			steal_suitable_fallback(zone, page, start_migratetype);
> @@ -2252,9 +2251,9 @@ struct page *buffered_rmqueue(struct zone *preferred_zone,
>  		}
>  
>  		if (cold)
> -			page = list_entry(list->prev, struct page, lru);
> +			page = list_last_entry(list, struct page, lru);
>  		else
> -			page = list_entry(list->next, struct page, lru);
> +			page = list_first_entry(list, struct page, lru);
>  
>  		list_del(&page->lru);
>  		pcp->count--;
> -- 
> 2.5.0
> 
> 
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-- 
Michal Hocko
SUSE Labs
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