linux-kernel - Re: [PATCH 0/3] makedumpfile: hugepage filtering for vmcore dump

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Date:	Fri, 29 Nov 2013 12:21:47 +0900
From:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
To:	Atsushi Kumagai <kumagai-atsushi@....nes.nec.co.jp>
CC:	"bhe@...hat.com" <bhe@...hat.com>,
	"tom.vaden@...com" <tom.vaden@...com>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"jingbai.ma@...com" <jingbai.ma@...com>,
	"ptesarik@...e.cz" <ptesarik@...e.cz>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"lisa.mitchell@...com" <lisa.mitchell@...com>,
	"anderson@...hat.com" <anderson@...hat.com>,
	"ebiederm@...ssion.com" <ebiederm@...ssion.com>,
	"vgoyal@...hat.com" <vgoyal@...hat.com>
Subject: Re: [PATCH 0/3] makedumpfile: hugepage filtering for vmcore dump

(2013/11/29 12:02), Atsushi Kumagai wrote:
> On 2013/11/28 16:50:21, kexec <kexec-bounces@...ts.infradead.org> wrote:
>>>> ping, in case you overlooked this...
>>>
>>> Sorry for the delayed response, I prioritize the release of v1.5.5 now.
>>>
>>> Thanks for your advice, check_cyclic_buffer_overrun() should be fixed
>>> as you said. In addition, I'm considering other way to address such case,
>>> that is to bring the number of "overflowed pages" to the next cycle and
>>> exclude them at the top of __exclude_unnecessary_pages() like below:
>>>
>>>                  /*
>>>                   * The pages which should be excluded still remain.
>>>                   */
>>>                  if (remainder >= 1) {
>>>                          int i;
>>>                          unsigned long tmp;
>>>                          for (i = 0; i < remainder; ++i) {
>>>                                  if (clear_bit_on_2nd_bitmap_for_kernel(pfn + i)) {
>>>                                          pfn_user++;
>>>                                          tmp++;
>>>                                  }
>>>                          }
>>>                          pfn += tmp;
>>>                          remainder -= tmp;
>>>                          mem_map += (tmp - 1) * SIZE(page);
>>>                          continue;
>>>                  }
>>>
>>> If this way works well, then aligning info->buf_size_cyclic will be
>>> unnecessary.
>>>
>>
>> I selected the current implementation of changing cyclic buffer size becuase
>> I thought it was simpler than carrying over remaining filtered pages to next cycle
>> in that there was no need to add extra code in filtering processing.
>>
>> I guess the reason why you think this is better now is how to detect maximum order of
>> huge page is hard in some way, right?
> 
> The maximum order will be gotten from HUGETLB_PAGE_ORDER or HPAGE_PMD_ORDER,
> so I don't say it's hard. However, the carrying over method doesn't depend on
> such kernel symbols, so I think it's robuster.
> 

Then, it's better to remove check_cyclic_buffer_overrun() and rewrite part of free page
filtering in __exclude_unnecessary_pages(). Could you do that too?

-- 
Thanks.
HATAYAMA, Daisuke

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