[PATCH v2] makedumpfile: Exclude unnecessary hugepages.

[Atsushi Kumagai]

Hello Baoquan,

>On 06/17/14 at 02:32am, Atsushi Kumagai wrote:
>> Hello,
>>
>>  		/*
>>  		 * 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, cycle))
>> -				pfn_user++;
>> +		else if (info->dump_level & DL_EXCLUDE_USER_DATA) {
>Hi Atsushi,
>
>Could it be changed to checking hugepage first, then anonymous page?
>This can avoid involving the free_huge_page.
>
>like this:
>	int nr_pages;
>	if (page_is_hugepage(flags) {
>		int nr_pages = 1 << compound_order;
>
>		exclude_range(&pfn_user, pfn, pfn + nr_pages, cycle);
>
>		pfn += nr_pages - 1;
>		mem_map += (nr_pages - 1) * SIZE(page);
>	} else if (isAnon(mapping)) {
>		int nr_pages = 1;
>
>		exclude_range(&pfn_user, pfn, pfn + nr_pages, cycle);
>
>		pfn += nr_pages - 1;
>		mem_map += (nr_pages - 1) * SIZE(page);
>	}
>
>But I may not know the meaning of free_huge_page completely. If you
>think introducing free_huge_page is better, I am fine too, can ACK that
>kernel patch to export free_huge_page you posted.

The assumption that all compound pages are user pages is wrong since some
kernel pages can be compound. For example, kmalloc_large_node() calls 
alloc_pages_node() with __GFP_COMP. This means we have to check compound
user pages without only depending on page_is_hugepage(). We can detect THPs
with the combination of page_is_hugepage() and isAnon(), but it can't be
applied to hugetlbfs pages.
This is why we need to export free_huge_page.

BTW, the v2 code can misdetect hugetlbfs due to the wrong check order, 
I'm going to fix it in the next version.


Thanks
Atsushi Kumagai

>Thanks
>Baoquan
>
>> +			/*
>> +			 * Exclude the anonymous pages as user pages.
>> +			 */
>> +			if (isAnon(mapping)) {
>> +				int nr_pages;
>> +				/*
>> +				 * Check the compound page
>> +				 */
>> +				if (page_is_hugepage(flags) && compound_order > 0)
>> +					nr_pages = 1 << compound_order;
>> +				else
>> +					nr_pages = 1;
>> +
>> +				exclude_range(&pfn_user, pfn, pfn + nr_pages, cycle);
>> +
>> +				pfn += nr_pages - 1;
>> +				mem_map += (nr_pages - 1) * SIZE(page);
>> +			}
>> +			/*
>> +			 * Exclude the hugetlbfs pages as user pages.
>> +			 */
>> +			else if (hugetlb_dtor == SYMBOL(free_huge_page)) {
>> +				int nr_pages = 1 << compound_order;
>> +
>> +				exclude_range(&pfn_user, pfn, pfn + nr_pages, cycle);
>> +
>> +				pfn += nr_pages - 1;
>> +				mem_map += (nr_pages - 1) * SIZE(page);
>> +			}
>>  		}
>
>_______________________________________________
>kexec mailing list
>kexec at lists.infradead.org
>http://lists.infradead.org/mailman/listinfo/kexec