Re: Suspicious error for CMA stress test

From: Hanjun Guo
Date: Fri Mar 04 2016 - 01:06:45 EST

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 <labbott@xxxxxxxxxx>:
>>>>> (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:

-bash-4.3# cat /proc/meminfo |grep Cma
CmaTotal: 204800 kB
CmaFree: 19388216 kB

-bash-4.3# cat /proc/meminfo
MemTotal: 16342016 kB
MemFree: 35146212 kB
MemAvailable: 35158008 kB
Buffers: 4236 kB
Cached: 45032 kB
SwapCached: 0 kB
Active: 19276 kB
Inactive: 36492 kB
Active(anon): 6724 kB
Inactive(anon): 52 kB
Active(file): 12552 kB
Inactive(file): 36440 kB
Unevictable: 0 kB
Mlocked: 0 kB
SwapTotal: 0 kB
SwapFree: 0 kB
Dirty: 0 kB
Writeback: 0 kB
AnonPages: 6524 kB
Mapped: 24724 kB
Shmem: 264 kB
Slab: 26948 kB
SReclaimable: 6260 kB
SUnreclaim: 20688 kB
KernelStack: 3296 kB
PageTables: 400 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
WritebackTmp: 0 kB
CommitLimit: 8171008 kB
Committed_AS: 32764 kB
VmallocTotal: 258998208 kB
VmallocUsed: 0 kB
VmallocChunk: 0 kB
AnonHugePages: 0 kB
CmaTotal: 204800 kB
CmaFree: 19388216 kB
HugePages_Total: 0
HugePages_Free: 0
HugePages_Rsvd: 0
HugePages_Surp: 0
Hugepagesize: 2048 kB

Thanks
Hanjun

>
> It checks problematic buddy merging and prevent it.
> I will try to find another way that is less intrusive for freepath performance.
>
> Thanks.
>
> ---------------->8-----------------------
> >From 855cb11368487a0f02a5ad5b3d9de375dfbb061c Mon Sep 17 00:00:00 2001
> From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> Date: Fri, 4 Mar 2016 13:28:17 +0900
> Subject: [PATCH] mm/cma: fix race
>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> ---
> mm/page_alloc.c | 14 ++++++++++----
> 1 file changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c6c38ed..a01c3b5 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 +644,12 @@ 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) &&
> + has_isolate_pageblock(zone) &&
> + order >= pageblock_order &&
> + is_migrate_isolate(get_pageblock_migratetype(buddy)))
> + return 0;
> +
> VM_BUG_ON_PAGE(page_count(buddy) != 0, buddy);
>
> return 1;
> @@ -711,7 +717,7 @@ 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 +751,7 @@ 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;