[PATCH 03/11] mm: mmzone: introduce zone_pfn_same_memmap()

[Michal Nazarewicz]

> On Fri, Nov 18, 2011 at 05:43:10PM +0100, Marek Szyprowski wrote:
>> From: Michal Nazarewicz <mina86 at mina86.com>
>> diff --git a/mm/compaction.c b/mm/compaction.c
>> index 6afae0e..09c9702 100644
>> --- a/mm/compaction.c
>> +++ b/mm/compaction.c
>> @@ -111,7 +111,10 @@ skip:
>>
>>  next:
>>  		pfn += isolated;
>> -		page += isolated;
>> +		if (zone_pfn_same_memmap(pfn - isolated, pfn))
>> +			page += isolated;
>> +		else
>> +			page = pfn_to_page(pfn);
>>  	}

On Mon, 12 Dec 2011 15:19:53 +0100, Mel Gorman <mel at csn.ul.ie> wrote:
> Is this necessary?
>
> We are isolating pages, the largest of which is a MAX_ORDER_NR_PAGES
> page.  [...]

This is not true for CMA.

> That said, everywhere else managed to avoid checks like this by always
> scanning in units of pageblocks. Maybe this should be structured
> the same way to guarantee pfn_valid is called at least per pageblock
> (even though only once per MAX_ORDER_NR_PAGES is necessary).

I'll look into that.

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