linux-kernel - Re: [RFC][PATCH] CMA: drivers/base/Kconfig: restrict CMA size to non-zero value

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Date:	Mon, 19 May 2014 18:14:14 +0900
From:	Gioh Kim <gioh.kim@....com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
CC:	Michal Nazarewicz <mina86@...a86.com>,
	Minchan Kim <minchan.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Laura Abbott <lauraa@...eaurora.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Heesub Shin <heesub.shin@...sung.com>,
	Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <hannes@...xchg.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	이건호 <gunho.lee@....com>, gurugio@...il.com
Subject: Re: [RFC][PATCH] CMA: drivers/base/Kconfig: restrict CMA size to
 non-zero value

In __dma_alloc function, your patch can make __alloc_from_pool work.
But __alloc_from_contiguous doesn't work.
Therefore __dma_alloc sometimes works and sometimes not according to the gfp(__GFP_WAIT) flag.
Do I understand correctly?

I think __dma_alloc should work consistently.
Both of __alloc_from_contiguous and __alloc_from_pool should work together,
or both of them do not work.


2014-05-19 오후 2:55, Joonsoo Kim 쓴 글:
> On Mon, May 19, 2014 at 10:47:12AM +0900, Gioh Kim wrote:
>> Thank you for your advice. I didn't notice it.
>>
>> I'm adding followings according to your advice:
>>
>> - range restrict for CMA_SIZE_MBYTES and *CMA_SIZE_PERCENTAGE*
>> I think this can prevent the wrong kernel option.
>>
>> - change size_cmdline into default value SZ_16M
>> I am not sure this can prevent if cma=0 cmdline option is also with base and limit options.
>
> Hello,
>
> I think that this problem is originated from atomic_pool_init().
> If configured coherent_pool size is larger than default cma size,
> it can be failed even if this patch is applied.
>
> How about below patch?
> It uses fallback allocation if CMA is failed.
>
> Thanks.
>
> -----------------8<---------------------
> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index 6b00be1..2909ab9 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -379,7 +379,7 @@ static int __init atomic_pool_init(void)
>          unsigned long *bitmap;
>          struct page *page;
>          struct page **pages;
> -       void *ptr;
> +       void *ptr = NULL;
>          int bitmap_size = BITS_TO_LONGS(nr_pages) * sizeof(long);
>
>          bitmap = kzalloc(bitmap_size, GFP_KERNEL);
> @@ -393,7 +393,7 @@ static int __init atomic_pool_init(void)
>          if (IS_ENABLED(CONFIG_DMA_CMA))
>                  ptr = __alloc_from_contiguous(NULL, pool->size, prot, &page,
>                                                atomic_pool_init);
> -       else
> +       if (!ptr)
>                  ptr = __alloc_remap_buffer(NULL, pool->size, gfp, prot, &page,
>                                             atomic_pool_init);
>          if (ptr) {
>
>
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