Subject: Suspicious error for CMA stress test

From: [email-masked] (Leizhen (ThunderTown))
Date: Mon, 7 Mar 2016 16:16:39 +0800

On 2016/3/7 12:34, Joonsoo Kim wrote:
> On Fri, Mar 04, 2016 at 03:35:26PM +0800, Hanjun Guo wrote:
>> On 2016/3/4 14:38, Joonsoo Kim wrote:
>>> On Fri, Mar 04, 2016 at 02:05:09PM +0800, Hanjun Guo wrote:
>>>> On 2016/3/4 12:32, Joonsoo Kim wrote:
>>>>> On Fri, Mar 04, 2016 at 11:02:33AM +0900, Joonsoo Kim wrote:
>>>>>> On Thu, Mar 03, 2016 at 08:49:01PM +0800, Hanjun Guo wrote:
>>>>>>> On 2016/3/3 15:42, Joonsoo Kim wrote:
>>>>>>>> 2016-03-03 10:25 GMT+09:00 Laura Abbott <[email-masked]>:
>>>>>>>>> (cc -mm and Joonsoo Kim)
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On 03/02/2016 05:52 AM, Hanjun Guo wrote:
>>>>>>>>>> Hi,
>>>>>>>>>>
>>>>>>>>>> I came across a suspicious error for CMA stress test:
>>>>>>>>>>
>>>>>>>>>> Before the test, I got:
>>>>>>>>>> -bash-4.3# cat /proc/meminfo | grep Cma
>>>>>>>>>> CmaTotal:         204800 kB
>>>>>>>>>> CmaFree:          195044 kB
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> After running the test:
>>>>>>>>>> -bash-4.3# cat /proc/meminfo | grep Cma
>>>>>>>>>> CmaTotal:         204800 kB
>>>>>>>>>> CmaFree:         6602584 kB
>>>>>>>>>>
>>>>>>>>>> So the freed CMA memory is more than total..
>>>>>>>>>>
>>>>>>>>>> Also the the MemFree is more than mem total:
>>>>>>>>>>
>>>>>>>>>> -bash-4.3# cat /proc/meminfo
>>>>>>>>>> MemTotal:       16342016 kB
>>>>>>>>>> MemFree:        22367268 kB
>>>>>>>>>> MemAvailable:   22370528 kB
>>>>>>> [...]
>>>>>>>>> I played with this a bit and can see the same problem. The sanity
>>>>>>>>> check of CmaFree < CmaTotal generally triggers in
>>>>>>>>> __move_zone_freepage_state in unset_migratetype_isolate.
>>>>>>>>> This also seems to be present as far back as v4.0 which was the
>>>>>>>>> first version to have the updated accounting from Joonsoo.
>>>>>>>>> Were there known limitations with the new freepage accounting,
>>>>>>>>> Joonsoo?
>>>>>>>> I don't know. I also played with this and looks like there is
>>>>>>>> accounting problem, however, for my case, number of free page is slightly less
>>>>>>>> than total. I will take a look.
>>>>>>>>
>>>>>>>> Hanjun, could you tell me your malloc_size? I tested with 1 and it doesn't
>>>>>>>> look like your case.
>>>>>>> I tested with malloc_size with 2M, and it grows much bigger than 1M, also I
>>>>>>> did some other test:
>>>>>> Thanks! Now, I can re-generate erronous situation you mentioned.
>>>>>>
>>>>>>>  - run with single thread with 100000 times, everything is fine.
>>>>>>>
>>>>>>>  - I hack the cam_alloc() and free as below [1] to see if it's lock issue, with
>>>>>>>    the same test with 100 multi-thread, then I got:
>>>>>> [1] would not be sufficient to close this race.
>>>>>>
>>>>>> Try following things [A]. And, for more accurate test, I changed code a bit more
>>>>>> to prevent kernel page allocation from cma area [B]. This will prevent kernel
>>>>>> page allocation from cma area completely so we can focus cma_alloc/release race.
>>>>>>
>>>>>> Although, this is not correct fix, it could help that we can guess
>>>>>> where the problem is.
>>>>> More correct fix is something like below.
>>>>> Please test it.
>>>> Hmm, this is not working:
>>> Sad to hear that.
>>>
>>> Could you tell me your system's MAX_ORDER and pageblock_order?
>>>
>>
>> MAX_ORDER is 11, pageblock_order is 9, thanks for your help!
> 
> Hmm... that's same with me.
> 
> Below is similar fix that prevents buddy merging when one of buddy's
> migrate type, but, not both, is MIGRATE_ISOLATE. In fact, I have
> no idea why previous fix (more correct fix) doesn't work for you.
> (It works for me.) But, maybe there is a bug on the fix
> so I make new one which is more general form. Please test it.

Hi,
	Hanjun Guo has gone to Tailand on business, so I help him to run this patch. The result
shows that the count of "CmaFree:" is OK now. But sometimes printed some information as below:

alloc_contig_range: [28500, 28600) PFNs busy
alloc_contig_range: [28300, 28380) PFNs busy

> 
> Thanks.
> 
> ---------->8-------------
>>>From dd41e348572948d70b935fc24f82c096ff0fb417 Mon Sep 17 00:00:00 2001
> From: Joonsoo Kim <[email-masked]>
> Date: Fri, 4 Mar 2016 13:28:17 +0900
> Subject: [PATCH] mm/cma: fix race
> 
> Signed-off-by: Joonsoo Kim <[email-masked]>
> ---
>  mm/page_alloc.c | 33 +++++++++++++++++++--------------
>  1 file changed, 19 insertions(+), 14 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c6c38ed..d80d071 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -620,8 +620,8 @@ static inline void rmv_page_order(struct page *page)
>   *
>   * For recording page's order, we use page_private(page).
>   */
> -static inline int page_is_buddy(struct page *page, struct page *buddy,
> -                                                       unsigned int order)
> +static inline int page_is_buddy(struct zone *zone, struct page *page,
> +                               struct page *buddy, unsigned int order)
>  {
>         if (!pfn_valid_within(page_to_pfn(buddy)))
>                 return 0;
> @@ -644,6 +644,20 @@ static inline int page_is_buddy(struct page *page, struct page *buddy,
>                 if (page_zone_id(page) != page_zone_id(buddy))
>                         return 0;
>  
> +               if (IS_ENABLED(CONFIG_CMA) &&
> +                       unlikely(has_isolate_pageblock(zone)) &&
> +                       unlikely(order >= pageblock_order)) {
> +                       int page_mt, buddy_mt;
> +
> +                       page_mt = get_pageblock_migratetype(page);
> +                       buddy_mt = get_pageblock_migratetype(buddy);
> +
> +                       if (page_mt != buddy_mt &&
> +                               (is_migrate_isolate(page_mt) ||
> +                               is_migrate_isolate(buddy_mt)))
> +                               return 0;
> +               }
> +
>                 VM_BUG_ON_PAGE(page_count(buddy) != 0, buddy);
>  
>                 return 1;
> @@ -691,17 +705,8 @@ static inline void __free_one_page(struct page *page,
>         VM_BUG_ON_PAGE(page->flags & PAGE_FLAGS_CHECK_AT_PREP, page);
>  
>         VM_BUG_ON(migratetype == -1);
> -       if (is_migrate_isolate(migratetype)) {
> -               /*
> -                * We restrict max order of merging to prevent merge
> -                * between freepages on isolate pageblock and normal
> -                * pageblock. Without this, pageblock isolation
> -                * could cause incorrect freepage accounting.
> -                */
> -               max_order = min_t(unsigned int, MAX_ORDER, pageblock_order + 1);
> -       } else {
> +       if (!is_migrate_isolate(migratetype))
>                 __mod_zone_freepage_state(zone, 1 << order, migratetype);
> -       }
>  
>         page_idx = pfn & ((1 << max_order) - 1);
>  
> @@ -711,7 +716,7 @@ static inline void __free_one_page(struct page *page,
>         while (order < max_order - 1) {
>                 buddy_idx = __find_buddy_index(page_idx, order);
>                 buddy = page + (buddy_idx - page_idx);
> -               if (!page_is_buddy(page, buddy, order))
> +               if (!page_is_buddy(zone, page, buddy, order))
>                         break;
>                 /*
>                  * Our buddy is free or it is CONFIG_DEBUG_PAGEALLOC guard page,
> @@ -745,7 +750,7 @@ static inline void __free_one_page(struct page *page,
>                 higher_page = page + (combined_idx - page_idx);
>                 buddy_idx = __find_buddy_index(combined_idx, order + 1);
>                 higher_buddy = higher_page + (buddy_idx - combined_idx);
> -               if (page_is_buddy(higher_page, higher_buddy, order + 1)) {
> +               if (page_is_buddy(zone, higher_page, higher_buddy, order + 1)) {
>                         list_add_tail(&page->lru,
>                                 &zone->free_area[order].free_list[migratetype]);
>                         goto out;
>