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

HATAYAMA Daisuke
2013-11-29T03:24:36Z

(2013/11/29 12:02), Atsushi Kumagai wrote:
> On 2013/11/28 16:50:21, kexec <kexec-bounces@lists.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