linux-kernel - Re: [PATCH v2 2/3] mm: cma: allocation trigger

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Message-ID: <54C7A9F6.1080500@oracle.com>
Date:	Tue, 27 Jan 2015 10:08:38 -0500
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
CC:	linux-kernel@...r.kernel.org, m.szyprowski@...sung.com,
	akpm@...ux-foundation.org, lauraa@...eaurora.org
Subject: Re: [PATCH v2 2/3] mm: cma: allocation trigger

On 01/27/2015 03:06 AM, Joonsoo Kim wrote:
> On Mon, Jan 26, 2015 at 09:26:04AM -0500, Sasha Levin wrote:
>> Provides a userspace interface to trigger a CMA allocation.
>>
>> Usage:
>>
>> 	echo [pages] > alloc
>>
>> This would provide testing/fuzzing access to the CMA allocation paths.
>>
>> Signed-off-by: Sasha Levin <sasha.levin@...cle.com>
>> ---
>>  mm/cma_debug.c |   60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++--
>>  1 file changed, 58 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/cma_debug.c b/mm/cma_debug.c
>> index 3a25413..39c7116 100644
>> --- a/mm/cma_debug.c
>> +++ b/mm/cma_debug.c
>> @@ -7,9 +7,22 @@
>>  
>>  #include <linux/debugfs.h>
>>  #include <linux/cma.h>
>> +#include <linux/list.h>
>> +#include <linux/kernel.h>
>> +#include <linux/dma-contiguous.h>
> 
> dma-contiguous.h doesn't needed now.

Right.

>> +#include <linux/slab.h>
>>  
>>  #include "cma.h"
>>  
>> +struct cma_mem {
>> +	struct hlist_node node;
>> +	struct page *p;
>> +	unsigned long n;
>> +};
>> +
>> +static HLIST_HEAD(cma_mem_head);
>> +static DEFINE_SPINLOCK(cma_mem_head_lock);
>> +
>>  static struct dentry *cma_debugfs_root;
> 
> How about keeping cma_mem_head on each cma area separately?

Good point, we're mixing allocations here.

>>  static int cma_debugfs_get(void *data, u64 *val)
>> @@ -23,8 +36,48 @@ static int cma_debugfs_get(void *data, u64 *val)
>>  
>>  DEFINE_SIMPLE_ATTRIBUTE(cma_debugfs_fops, cma_debugfs_get, NULL, "%llu\n");
>>  
>> -static void cma_debugfs_add_one(struct cma *cma, int idx)
>> +static void cma_add_to_cma_mem_list(struct cma_mem *mem)
>> +{
>> +	spin_lock(&cma_mem_head_lock);
>> +	hlist_add_head(&mem->node, &cma_mem_head);
>> +	spin_unlock(&cma_mem_head_lock);
>> +}
>> +
>> +static int cma_alloc_mem(struct cma *cma, int count)
>>  {
>> +	struct cma_mem *mem;
>> +	struct page *p;
>> +
>> +	mem = kzalloc(sizeof(*mem), GFP_KERNEL);
>> +	if (!mem)
>> +		return -ENOMEM;
>> +
>> +	p = cma_alloc(cma, count, CONFIG_CMA_ALIGNMENT);
>> +	if (!p) {
>> +		kfree(mem);
>> +		return -ENOMEM;
>> +	}
> 
> CONFIG_CMA_ALIGNMENT looks not good. It means just maximum aligment
> so it is odd to use this value in testing. Is there special meaning
> to use it here?

No good reason, I stole that from a different piece of code.

> Could we also get alignment parameter from user? Something like below.
> 
> echo "4 1" > alloc
> 4 for number of pages
> 1 for alignment.
> 
> If it is impossible, just 0 looks better than CONFIG_CMA_ALIGNMENT.

I'd rather keep it simple and use a single parameter for now.


Thanks,
Sasha
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