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Date: Mon, 15 Feb 2016 18:06:08 +0800
From: Xishi Qiu <qiuxishi@huawei.com>
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To: Joonsoo Kim <iamjoonsoo.kim@lge.com>
CC: zhong jiang <zhongjiang@huawei.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Vlastimil Babka <vbabka@suse.cz>, Aaron Lu <aaron.lu@intel.com>,
        Mel Gorman <mgorman@suse.de>, Rik van Riel <riel@redhat.com>,
        David Rientjes <rientjes@google.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux Memory Management List <linux-mm@kvack.org>
Subject: Re: [PATCH v2 3/3] mm/compaction: speed up pageblock_pfn_to_page()
 when zone is contiguous
References: <1454566775-30973-1-git-send-email-iamjoonsoo.kim@lge.com> <1454566775-30973-3-git-send-email-iamjoonsoo.kim@lge.com> <20160204164929.a2f12b8a7edcdfa596abd850@linux-foundation.org> <CAAmzW4Pps1gSXb5qCvbkC=wNjcySgVYZu1jLeBWy31q7RNWVYg@mail.gmail.com> <56C0550F.8020402@huawei.com> <20160215024220.GA30918@js1304-P5Q-DELUXE>
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On 2016/2/15 10:42, Joonsoo Kim wrote:

>>
>> I have a question about the zone continuity. because hole exists at
>> arbitrary position in a page block. Therefore, only pageblock_pf_to_page()
>> is insufficiency, whether pageblock aligned pfn or not , the pfn_valid_within()
>> is necessary.
>>
>> eh: 120M-122M is a range of page block, but the 120.5M-121.5M is holes, only by
>> pageblock_pfn_to_page() to conclude in the result is inaccurate
> 
> contiguous may be misleading word. It doesn't represent there are no
> hole. It only represents that all pageblocks within zone span belong to
> corresponding zone and validity of all pageblock aligned pfn is
> checked. So, if it is set, we can safely call pfn_to_page() for pageblock
> aligned pfn in that zone without checking pfn_valid().
> 
> Thanks.
> 

Hi Joonsoo,

So "contiguous" here only means that struct page is exist, and don't care whether
the memory is exist, right?

Thanks,
Xishi Qiu

> 
> .
>