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

[HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>]

(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...

-- 
Thanks.
HATAYAMA, Daisuke