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

[Jaewon Kim]

On 2017ë 01ì 02ì 15:46, Michal Nazarewicz wrote:
> On Mon, Jan 02 2017, Jaewon Kim wrote:
>> There are many reasons of CMA allocation failure such as EBUSY, ENOMEM, EINTR.
>> But we did not know error reason so far. This patch prints the error value.
>>
>> Additionally if CONFIG_CMA_DEBUG is enabled, this patch shows bitmap status to
>> know available pages. Actually CMA internally tries on all available regions
>> because some regions can be failed because of EBUSY. Bitmap status is useful to
>> know in detail on both ENONEM and EBUSY;
>>  ENOMEM: not tried at all because of no available region
>>          it could be too small total region or could be fragmentation issue
>>  EBUSY:  tried some region but all failed
>>
>> This is an ENOMEM example with this patch.
>> [   12.415458]  [2:   Binder:714_1:  744] cma: cma_alloc: alloc failed, req-size: 256 pages, ret: -12
>> If CONFIG_CMA_DEBUG is enabled, avabile pages also will be shown as concatenated
>> size@position format. So 4@572 means that there are 4 available pages at 572
>> position starting from 0 position.
>> [   12.415503]  [2:   Binder:714_1:  744] cma: number of available pages: 4@572+7@585+7@601+8@632+38@730+166@1114+127@1921=> 357 free of 2048 total pages
>>
>> Signed-off-by: Jaewon Kim <jaewon31.kim@xxxxxxxxxxx>
>> Acked-by: Michal Nazarewicz <mina86@xxxxxxxxxx>
>> ---
>>  mm/cma.c | 34 +++++++++++++++++++++++++++++++++-
>>  1 file changed, 33 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/cma.c b/mm/cma.c
>> index c960459..9e037541 100644
>> --- a/mm/cma.c
>> +++ b/mm/cma.c
>> @@ -353,6 +353,32 @@ int __init cma_declare_contiguous(phys_addr_t base,
>>      return ret;
>>  }
>>  
>> +#ifdef CONFIG_CMA_DEBUG
>> +static void debug_show_cma_areas(struct cma *cma)
> Make it âcma_debug_show_areasâ.  All other functions have âcmaâ as
> prefix so thatâs more consistent.
OK no problem.
>
>> +{
>> +    unsigned long next_zero_bit, next_set_bit;
>> +    unsigned long start = 0;
>> +    unsigned int nr_zero, nr_total = 0;
>> +
>> +    mutex_lock(&cma->lock);
>> +    pr_info("number of available pages: ");
>> +    for (;;) {
>> +        next_zero_bit = find_next_zero_bit(cma->bitmap, cma->count, start);
>> +        if (next_zero_bit >= cma->count)
>> +            break;
>> +        next_set_bit = find_next_bit(cma->bitmap, cma->count, next_zero_bit);
>> +        nr_zero = next_set_bit - next_zero_bit;
>> +        pr_cont("%s%u@%lu", nr_total ? "+" : "", nr_zero, next_zero_bit);
>> +        nr_total += nr_zero;
>> +        start = next_zero_bit + nr_zero;
>> +    }
>> +    pr_cont("=> %u free of %lu total pages\n", nr_total, cma->count);
>> +    mutex_unlock(&cma->lock);
>> +}
>> +#else
>> +static inline void debug_show_cma_areas(struct cma *cma) { }
>> +#endif
>> +
>>  /**
>>   * cma_alloc() - allocate pages from contiguous area
>>   * @cma:   Contiguous memory region for which the allocation is performed.
>> @@ -369,7 +395,7 @@ 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;
>> @@ -426,6 +452,12 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align)
>>  
>>      trace_cma_alloc(pfn, page, count, align);
>>  
>> +    if (ret) {
>> +        pr_info("%s: alloc failed, req-size: %zu pages, ret: %d\n",
>> +            __func__, count, ret);
>> +        debug_show_cma_areas(cma);
>> +    }
>> +
>>      pr_debug("%s(): returned %p\n", __func__, page);
>>      return page;
>>  }
>> -- 
>>

Added the latest.