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Message-ID: <520C7780.7020008@huawei.com>
Date: Thu, 15 Aug 2013 14:38:56 +0800
From: Xishi Qiu <qiuxishi@huawei.com>
MIME-Version: 1.0
Subject: Re: [PATCH] mm: skip the page buddy block instead of one page
References: <520B0B75.4030708@huawei.com> <20130814085711.GK2296@suse.de> <20130814155205.GA2706@gmail.com> <20130814161642.GM2296@suse.de> <20130814163921.GC2706@gmail.com> <20130814180012.GO2296@suse.de> <520C3DD2.8010905@huawei.com> <20130815024427.GA2718@gmail.com> <520C4EFF.8040305@huawei.com> <20130815041736.GA2592@gmail.com>
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Sender: owner-linux-mm@kvack.org
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To: Minchan Kim <minchan@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>, Andrew Morton <akpm@linux-foundation.org>, riel@redhat.com, aquini@redhat.com, linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>

On 2013/8/15 12:17, Minchan Kim wrote:

> 
> Please read full thread in detail.
> 
> Mel suggested following as
> 
> if (PageBuddy(page)) {
>         int nr_pages = (1 << page_order(page)) - 1;
>         if (PageBuddy(page)) {
>                 nr_pages = min(nr_pages, MAX_ORDER_NR_PAGES - 1);
>                 low_pfn += nr_pages;
>                 continue;
>         }
> }
> 
> min(nr_pages, xxx) removes your concern but I think Mel's version
> isn't right. It should be aligned with pageblock boundary so I 
> suggested following.
> 
> if (PageBuddy(page)) {
> #ifdef CONFIG_MEMORY_ISOLATION
> 	unsigned long order = page_order(page);
> 	if (PageBuddy(page)) {
> 		low_pfn += (1 << order) - 1;
> 		low_pfn = min(low_pfn, end_pfn);

Hi Minchan,

I understand now, but why use "end_pfn" here? 
Do you mean we should use pageblock_nr_pages instead of MAX_ORDER_NR_PAGES?
Just like this:

if (PageBuddy(page)) {
	unsigned long order = page_order(page);
	order = min(order, pageblock_order);
	if (PageBuddy(page))
		low_pfn += (1 << order) - 1;
	continue;
}

Thanks,
Xishi Qiu

> 	}
> #endif
> 	continue;
> }
> 
> so worst case is (pageblock_nr_pages - 1).
> but we don't need to add CONFIG_MEMORY_ISOLATION so my suggestion
> is following as.
> 
> if (PageBuddy(page)) {
> 	unsigned long order = page_order(page);
> 	if (PageBuddy(page)) {
> 		low_pfn += (1 << order) - 1;
> 		low_pfn = min(low_pfn, end_pfn);
> 	}
> 	continue;
> }
> 
> 



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