linux-kernel - Re: [PATCH -mm v2] mm: have order > 0 compaction start off where it left

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Date:	Mon, 02 Jul 2012 20:57:03 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Sasha Levin <levinsasha928@...il.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Mel Gorman <mel@....ul.ie>,
	jaschut@...dia.gov, minchan@...nel.org,
	kamezawa.hiroyu@...fujitsu.com, Dave Jones <davej@...hat.com>
Subject: Re: [PATCH -mm v2] mm: have order > 0 compaction start off where
 it left

On 07/02/2012 01:42 PM, Sasha Levin wrote:
> On Thu, 2012-06-28 at 14:35 -0700, Andrew Morton wrote:
>> On Thu, 28 Jun 2012 17:24:25 -0400 Rik van Riel<riel@...hat.com>  wrote:
>>>
>>>>> @@ -463,6 +474,8 @@ static void isolate_freepages(struct zone *zone,
>>>>>              */
>>>>>             if (isolated)
>>>>>                     high_pfn = max(high_pfn, pfn);
>>>>> +          if (cc->order>   0)
>>>>> +                  zone->compact_cached_free_pfn = high_pfn;
>>>>
>>>> Is high_pfn guaranteed to be aligned to pageblock_nr_pages here?  I
>>>> assume so, if lots of code in other places is correct but it's
>>>> unobvious from reading this function.
>>>
>>> Reading the code a few more times, I believe that it is
>>> indeed aligned to pageblock size.
>>
>> I'll slip this into -next for a while.
>>
>> --- a/mm/compaction.c~isolate_freepages-check-that-high_pfn-is-aligned-as-expected
>> +++ a/mm/compaction.c
>> @@ -456,6 +456,7 @@ static void isolate_freepages(struct zon
>>                  }
>>                  spin_unlock_irqrestore(&zone->lock, flags);
>>
>> +               WARN_ON_ONCE(high_pfn&  (pageblock_nr_pages - 1));
>>                  /*
>>                   * Record the highest PFN we isolated pages from. When next
>>                   * looking for free pages, the search will restart here as
>
> I've triggered the following with today's -next:

I've been staring at the migrate code for most of the afternoon,
and am not sure how this is triggered.

At this point, I'm going to focus my attention on addressing
Minchan's comments on my code, and hoping someone who is more
familiar with the migrate code knows how high_pfn ends up
being not pageblock_nr_pages aligned...

-- 
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