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

HATAYAMA Daisuke
2013-11-28T07:50:09Z

(2013/11/28 16:08), Atsushi Kumagai wrote:
> On 2013/11/22 16:18:20, kexec <kexec-bounces@lists.infradead.org> wrote:
>> (2013/11/07 9:54), HATAYAMA Daisuke wrote:
>>> (2013/11/06 11:21), Atsushi Kumagai wrote:
>>>> (2013/11/06 5:27), Vivek Goyal wrote:
>>>>> On Tue, Nov 05, 2013 at 09:45:32PM +0800, Jingbai Ma wrote:
>>>>>> This patch set intend to exclude unnecessary hugepages from vmcore dump file.
>>>>>>
>>>>>> This patch requires the kernel patch to export necessary data structures into
>>>>>> vmcore: "kexec: export hugepage data structure into vmcoreinfo"
>>>>>> http://lists.infradead.org/pipermail/kexec/2013-November/009997.html
>>>>>>
>>>>>> This patch introduce two new dump levels 32 and 64 to exclude all unused and
>>>>>> active hugepages. The level to exclude all unnecessary pages will be 127 now.
>>>>>
>>>>> Interesting. Why hugepages should be treated any differentely than normal
>>>>> pages?
>>>>>
>>>>> If user asked to filter out free page, then it should be filtered and
>>>>> it should not matter whether it is a huge page or not?
>>>>
>>>> I'm making a RFC patch of hugepages filtering based on such policy.
>>>>
>>>> I attach the prototype version.
>>>> It's able to filter out also THPs, and suitable for cyclic processing
>>>> because it depends on mem_map and looking up it can be divided into
>>>> cycles. This is the same idea as page_is_buddy().
>>>>
>>>> So I think it's better.
>>>>
>>>
>>>> @@ -4506,14 +4583,49 @@ __exclude_unnecessary_pages(unsigned long mem_map,
>>>> && !isAnon(mapping)) {
>>>> if (clear_bit_on_2nd_bitmap_for_kernel(pfn))
>>>> pfn_cache_private++;
>>>> + /*
>>>> + * NOTE: If THP for cache is introduced, the check for
>>>> + * compound pages is needed here.
>>>> + */
>>>> }
>>>> /*
>>>> * Exclude the data page of the user process.
>>>> */
>>>> - else if ((info->dump_level & DL_EXCLUDE_USER_DATA)
>>>> - && isAnon(mapping)) {
>>>> - if (clear_bit_on_2nd_bitmap_for_kernel(pfn))
>>>> - pfn_user++;
>>>> + else if (info->dump_level & DL_EXCLUDE_USER_DATA) {
>>>> + /*
>>>> + * Exclude the anonnymous pages as user pages.
>>>> + */
>>>> + if (isAnon(mapping)) {
>>>> + if (clear_bit_on_2nd_bitmap_for_kernel(pfn))
>>>> + pfn_user++;
>>>> +
>>>> + /*
>>>> + * Check the compound page
>>>> + */
>>>> + if (page_is_hugepage(flags) && compound_order > 0) {
>>>> + int i, nr_pages = 1 << compound_order;
>>>> +
>>>> + for (i = 1; i < nr_pages; ++i) {
>>>> + if (clear_bit_on_2nd_bitmap_for_kernel(pfn + i))
>>>> + pfn_user++;
>>>> + }
>>>> + pfn += nr_pages - 2;
>>>> + mem_map += (nr_pages - 1) * SIZE(page);
>>>> + }
>>>> + }
>>>> + /*
>>>> + * Exclude the hugetlbfs pages as user pages.
>>>> + */
>>>> + else if (hugetlb_dtor == SYMBOL(free_huge_page)) {
>>>> + int i, nr_pages = 1 << compound_order;
>>>> +
>>>> + for (i = 0; i < nr_pages; ++i) {
>>>> + if (clear_bit_on_2nd_bitmap_for_kernel(pfn + i))
>>>> + pfn_user++;
>>>> + }
>>>> + pfn += nr_pages - 1;
>>>> + mem_map += (nr_pages - 1) * SIZE(page);
>>>> + }
>>>> }
>>>> /*
>>>> * Exclude the hwpoison page.
>>>
>>> I'm concerned about the case that filtering is not performed to part of mem_map
>>> entries not belonging to the current cyclic range.
>>>
>>> If maximum value of compound_order is larger than maximum value of
>>> CONFIG_FORCE_MAX_ZONEORDER, which makedumpfile obtains by ARRAY_LENGTH(zone.free_area),
>>> it's necessary to align info->bufsize_cyclic with larger one in
>>> check_cyclic_buffer_overrun().
>>>
>>
>> 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?

--
Thanks.
HATAYAMA, Daisuke