linux-kernel - Re: [PATCH] mm: skip the page buddy block instead of one page

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Date:	Thu, 15 Aug 2013 14:38:56 +0800
From:	Xishi Qiu <qiuxishi@...wei.com>
To:	Minchan Kim <minchan@...nel.org>
CC:	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>, <riel@...hat.com>,
	<aquini@...hat.com>, <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: skip the page buddy block instead of one page

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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