RE: NR_FREE_CMA_PAGES larger than total CMA size

[Lisa Du <cldu@marvell.com>]

>-----Original Message-----
>From: Joonsoo Kim [mailto:iamjoonsoo.kim@lge.com]
>Sent: 2014年7月7日 12:54
>To: Lisa Du
>Cc: linux-mm@kvack.org
>Subject: Re: NR_FREE_CMA_PAGES larger than total CMA size
>
>On Sat, Jul 05, 2014 at 01:13:17AM -0700, Lisa Du wrote:
>> Dear Sir
>> Recently I met one issue that after system run for a long time, free
>> cma pages recorded in vm_stat[NR_FREE_CMA_PAGES] are larger than total CMA size declared.
>> For example, I declared 64MB CMA size, but found free cma was 70MB.
>>
>> I added some trace to track how it happen, and found the reason maybe like below:
>> 1) alloc_contig_range() want to allocate a range [start, end], for
>> example [0x1e040, 0x1e050];
>>
>> 2) start_isolate_page_range() will isolate the range [pfn_max_align_down(start),
>>   pfn_max_align_up(end)]; for this example it's [0x1e000, 0x1e400]
>> (MAX_ORDER is 11);
>>
>> 3) drain_all_pages() would be called as follows, if there's some pages belong to the range
>>   [0x1e000, 0x1e400] was freed from the pcp_list, also if the page was MIGRATE_CMA,
>>   then vm_stat[NR_FREE_CMA_PAGES] would increase and also
>> NR_FREE_PAGES;
>>
>> 4) if the freed pages in #3 was not the range of [start, end], then at last undo_isolate_page_range()
>>   will be called, and the pages would be calculated again as free pages in unset_migratetype_isolate(),
>>   and __mod_zone_freepage_state() will increased again for these pages for both NR_FREE_CMA_PAGES
>>   and NR_FREE_PAGES.
>>   The function calling flow as below, the free pages in move_freepages() was calculated again.
>>   undo_isolate_page_range()
>> 	--> unset_migratetype_isolate()
>> 		--> move_freepages_block()
>> 			--> move_freepages()
>> 	--> __mod_zone_freepage_state()
>>
>> Shall we add some check in move_freepages() if the page was already in
>> CMA free list, then exclude it from the pages_moved?
>>
>> I found this issue in kernel v3.4, but seems there's no fix in latest kernel code base.
>> Not sure if anyone else has met such issue? Anyone would help to comment? Thanks a lot!
>
>Hello,
>
>Maybe this bug is relevant for my recent patchset.
>I don't have much time to investigate your problem, so if you have interest on my patchset, please look at it on below link
>
>https://lkml.org/lkml/2014/7/4/79
>
>If they work for you, please let me know. :)
Below patches works for me, thanks a lot!
  mm/page_alloc: handle page on pcp correctly if it's pageblock is isolated
  mm/page_alloc: carefully free the page on isolate pageblock
>
>Thanks.