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Date: Thu, 20 Dec 2012 12:26:01 -0500
From: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
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Subject: Re: [PATCH] mm: fix zone_watermark_ok_safe() accounting of isolated
 pages
References: <201212181018.41753.b.zolnierkie@samsung.com> <20121220005704.GA2556@blaptop>
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To: Minchan Kim <minchan@kernel.org>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>, Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org, Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@suse.cz>, Marek Szyprowski <m.szyprowski@samsung.com>, Michal Nazarewicz <mina86@mina86.com>, Hugh Dickins <hughd@google.com>, Kyungmin Park <kyungmin.park@samsung.com>, Tomasz Stanislawski <t.stanislaws@samsung.com>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, Aaditya Kumar <aaditya.kumar.30@gmail.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, kosaki.motohiro@gmail.com

> 2. Another approach. Let's avoid a branch in free_one_page if we don't enable
>    CONFIG_MEMORY_ISOLATION? It's simpler/less-churning/more accurate/removing
>    unnecessary codes compared to 1.
> 
> index 7e208f0..35c0e82 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -683,8 +683,12 @@ static void free_one_page(struct zone *zone, struct page *page, int order,
>         zone->pages_scanned = 0;
>  
>         __free_one_page(page, zone, order, migratetype);
> +#ifdef CONFIG_MEMORY_ISOLATION
>         if (unlikely(migratetype != MIGRATE_ISOLATE))
>                 __mod_zone_freepage_state(zone, 1 << order, migratetype);
> +#else
> +       __mod_zone_freepage_state(zone, 1 << order, migratetype);
> +#endif
>         spin_unlock(&zone->lock);
>  }
> 
> So I will
> 
> Acked-by: Minchan Kim <minchan@kernel.org>
> 
> Then, will send 2 as follow-up patch soon if anyone doesn't oppose.

I agree. I guess we can remove this branch completely from free page fast path.
However your patch is good first step.


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