linux-kernel - Re: [Linaro-mm-sig] [PATCH] mm: skip watermarks check for already isolated blocks in split_free

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Message-ID: <50A7D524.2060809@gmail.com>
Date:	Sat, 17 Nov 2012 19:19:16 +0100
From:	Francesco Lavra <francescolavra.fl@...il.com>
To:	Marek Szyprowski <m.szyprowski@...sung.com>
CC:	linux-mm@...ck.org, linaro-mm-sig@...ts.linaro.org,
	linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Mel Gorman <mel@....ul.ie>,
	Michal Nazarewicz <mina86@...a86.com>,
	Minchan Kim <minchan@...nel.org>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [Linaro-mm-sig] [PATCH] mm: skip watermarks check for already
 isolated blocks in split_free_page()

Hi,

On 11/08/2012 07:59 AM, Marek Szyprowski wrote:
> Since commit 2139cbe627b8 ("cma: fix counting of isolated pages") free
> pages in isolated pageblocks are not accounted to NR_FREE_PAGES counters,
> so watermarks check is not required if one operates on a free page in
> isolated pageblock.
> 
> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
> ---
>  mm/page_alloc.c |   10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index fd154fe..43ab09f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1394,10 +1394,12 @@ int capture_free_page(struct page *page, int alloc_order, int migratetype)
>  	zone = page_zone(page);
>  	order = page_order(page);
>  
> -	/* Obey watermarks as if the page was being allocated */
> -	watermark = low_wmark_pages(zone) + (1 << order);
> -	if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
> -		return 0;
> +	if (get_pageblock_migratetype(page) != MIGRATE_ISOLATE) {

get_pageblock_migratetype(page) is also called later on in this function
and assigned to the mt variable: maybe the assignment should be moved
before (or inside) the above line?

--
Francesco
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