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

[Michal Hocko <mhocko@kernel.org>]

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?
 
> Signed-off-by: Jaewon Kim <jaewon31.kim@samsung.com>
> ---
>  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: ");
> +		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);
> +			nr_total += nr;
> +			start = bitmap_no + nr;
> +		}
> +		printk("=>%u pages, total: %lu pages\n", nr_total, cma->count);
> +		mutex_unlock(&cma->lock);
> +	}
> +
>  	return page;
>  }
>  
> -- 
> 1.9.1
> 
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-- 
Michal Hocko
SUSE Labs

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