Re: [PATCH] mm: cma: print allocation failure reason and bitmap status

[Jaewon Kim]

On 2016ë 12ì 29ì 18:43, Michal Hocko wrote:
> On Thu 29-12-16 18:26:38, Jaewon Kim wrote:
>>
>> On 2016ë 12ì 29ì 18:14, Michal Hocko wrote:
>>> On Thu 29-12-16 11:28:02, Jaewon Kim wrote:
>>>> There are many reasons of CMA allocation failure such as EBUSY, ENOMEM, EINTR.
>>>> This patch prints the error value and bitmap status to know available pages
>>>> regarding fragmentation.
>>>>
>>>> This is an ENOMEM example with this patch.
>>>> [   11.616321]  [2:   Binder:711_1:  740] cma: cma_alloc: alloc failed, req-size: 256 pages, ret: -12
>>>> [   11.616365]  [2:   Binder:711_1:  740] number of available pages: 4+7+7+8+38+166+127=>357 pages, total: 2048 pages
>>> Could you be more specific why this part is useful?
>> Hi
>> Without this patch we do not know why CMA allocation failed.
> Yes, I understand the first part
>
>> Additionally in case of ENOMEM, with bitmap status we can figure out that
> The code doesn't seem to check for ENOMEM though
Yes actually I wanted to look both ENOMEM case and EBUSY case.
Even in EBUSY case, we can look how much available pages existed, but all failed on those region because of EBUSY.
We may not need EINTR case, but I hope to look.
>
>> if it is too small CMA region issue or if it is fragmentation issue.
> then please describe that in the changelog. If I got it right the above
> would tell us that the fragmentation is the problem, right?
Yes fragmentation can be A problem, but bitmap status will explain EBUSY case too as I explained above.
>
>>>  
>>>> Signed-off-by: Jaewon Kim <jaewon31.kim@xxxxxxxxxxx>
>>>> ---
>>>>  mm/cma.c | 29 ++++++++++++++++++++++++++++-
>>>>  1 file changed, 28 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/mm/cma.c b/mm/cma.c
>>>> index c960459..535aa39 100644
>>>> --- a/mm/cma.c
>>>> +++ b/mm/cma.c
>>>> @@ -369,7 +369,7 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align)
>>>>  	unsigned long start = 0;
>>>>  	unsigned long bitmap_maxno, bitmap_no, bitmap_count;
>>>>  	struct page *page = NULL;
>>>> -	int ret;
>>>> +	int ret = -ENOMEM;
>>>>  
>>>>  	if (!cma || !cma->count)
>>>>  		return NULL;
>>>> @@ -427,6 +427,33 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align)
>>>>  	trace_cma_alloc(pfn, page, count, align);
>>>>  
>>>>  	pr_debug("%s(): returned %p\n", __func__, page);
>>>> +
>>>> +	if (ret != 0) {
>>>> +		unsigned int nr, nr_total = 0;
>>>> +		unsigned long next_set_bit;
>>>> +
>>>> +		pr_info("%s: alloc failed, req-size: %zu pages, ret: %d\n",
>>>> +			__func__, count, ret);
>>>> +		mutex_lock(&cma->lock);
>>>> +		printk("number of available pages: ");
> I guess you want pr_info (or maybe pr_debug) here
Thank you I will change as you and Michal Nazarewichz commented.
>
>>>> +		start = 0;
>>>> +		for (;;) {
>>>> +			bitmap_no = find_next_zero_bit(cma->bitmap, cma->count, start);
>>>> +			next_set_bit = find_next_bit(cma->bitmap, cma->count, bitmap_no);
>>>> +			nr = next_set_bit - bitmap_no;
>>>> +			if (bitmap_no >= cma->count)
>>>> +				break;
>>>> +			if (nr_total == 0)
>>>> +				printk("%u", nr);
>>>> +			else
>>>> +				printk("+%u", nr);
> pr_cont
>
>>>> +			nr_total += nr;
>>>> +			start = bitmap_no + nr;
>>>> +		}
>>>> +		printk("=>%u pages, total: %lu pages\n", nr_total, cma->count);
> pr_cont
>
>>>> +		mutex_unlock(&cma->lock);
>>>> +	}
>>>> +
>>>>  	return page;
>>>>  }
>>>>  
>>>> -- 
>>>> 1.9.1
>>>>
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