linux-kernel - Re: [PATCH] switch free memory back to MIGRATE

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Date:	Mon, 13 Jul 2009 11:47:46 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Shaohua Li <shaohua.li@...el.com>
Cc:	kosaki.motohiro@...fujitsu.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, mel@....ul.ie, akpm@...ux-foundation.org
Subject: Re: [PATCH] switch free memory back to MIGRATE_MOVABLE

> When page is back to buddy and its order is bigger than pageblock_order, we can
> switch its type to MIGRATE_MOVABLE. This can reduce fragmentation. The patch
> has obvious effect when read a block device and then drop caches.
> 
> Signed-off-by: Shaohua Li <shaohua.li@...el.com>

This patch change hot path, but there is no performance mesurement description.
Also, I don't like modification buddy core for only drop caches.



> ---
>  mm/page_alloc.c |    9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> Index: linux/mm/page_alloc.c
> ===================================================================
> --- linux.orig/mm/page_alloc.c	2009-07-10 11:36:07.000000000 +0800
> +++ linux/mm/page_alloc.c	2009-07-13 09:25:21.000000000 +0800
> @@ -475,6 +475,15 @@ static inline void __free_one_page(struc
>  		order++;
>  	}
>  	set_page_order(page, order);
> +
> +	if (order >= pageblock_order && migratetype != MIGRATE_MOVABLE) {
> +		int i;
> +
> +		migratetype = MIGRATE_MOVABLE;
> +		for (i = 0; i < (1 << (order - pageblock_order)); i++)
> +			set_pageblock_migratetype(page +
> +				i * pageblock_nr_pages, MIGRATE_MOVABLE);
> +	}
>  	list_add(&page->lru,
>  		&zone->free_area[order].free_list[migratetype]);
>  	zone->free_area[order].nr_free++;
> --
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