linux-kernel - Re: [RFC 1/2] staging: ion: shrink page-pool by page unit

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Date:	Fri, 24 Oct 2014 08:31:52 +0900
From:	Gioh Kim <gioh.kim@....com>
To:	Devendra Naga <devendranaga4@...il.com>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	John Stultz <john.stultz@...aro.org>,
	Rebecca Schultz Zavin <rebecca@...roid.com>,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
	gunho.lee@....com
Subject: Re: [RFC 1/2] staging: ion: shrink page-pool by page unit



2014-10-24 오전 8:16, Gioh Kim 쓴 글:
>
>
> 2014-10-24 오전 5:36, Devendra Naga 쓴 글:
>> Hello,
>>
>> On Thu, Oct 23, 2014 at 6:22 PM, Gioh Kim <gioh.kim@....com> wrote:
>>> This patch shrink page-pool by page unit.
>>>
>>> Signed-off-by: Gioh Kim <gioh.kim@....com>
>>> ---
>>>   drivers/staging/android/ion/ion_page_pool.c   |    5 +++--
>>>   drivers/staging/android/ion/ion_system_heap.c |    7 +++++--
>>>   2 files changed, 8 insertions(+), 4 deletions(-)
>>
>>>
>>
>> --- cut --
>>
>>> diff --git a/drivers/staging/android/ion/ion_system_heap.c b/drivers/staging/android/ion/ion_system_heap.c
>>> index da2a63c..36e73c3 100644
>>> --- a/drivers/staging/android/ion/ion_system_heap.c
>>> +++ b/drivers/staging/android/ion/ion_system_heap.c
>>> @@ -211,7 +211,7 @@ static int ion_system_heap_shrink(struct ion_heap *heap, gfp_t gfp_mask,
>>>                                          int nr_to_scan)
>>>   {
>>>          struct ion_system_heap *sys_heap;
>>> -       int nr_total = 0;
>>> +       int nr_total = 0, nr_freed;
>>>          int i;
>>>
>>>          sys_heap = container_of(heap, struct ion_system_heap, heap);
>>> @@ -219,7 +219,10 @@ static int ion_system_heap_shrink(struct ion_heap *heap, gfp_t gfp_mask,
>>>          for (i = 0; i < num_orders; i++) {
>>>                  struct ion_page_pool *pool = sys_heap->pools[i];
>>>
>>> -               nr_total += ion_page_pool_shrink(pool, gfp_mask, nr_to_scan);
>>> +               nr_freed += ion_page_pool_shrink(pool, gfp_mask, nr_to_scan);
>>
>> nr_freed is not initialised to zero. This might result in updating of
>> a garbage value stored initially after nr_freed is created.
>
> Yes, your're right. It's my mistake.
> I testes this on my platform with custom kernel and copied codes.
> I missed a line for it.
> I'm sorry.

Following is the correct code:
nr_freed = ion_page_pool_shrink(pool, gfp_mask, nr_to_scan);

>
>>
>>> +               nr_total += nr_freed;
>>> +               /* nr_to_scan can be negative */
>>> +               nr_to_scan -= nr_freed;
>>>          }
>>>
>>>          return nr_total;
>>> --
>>> 1.7.9.5
>>>
>>> --
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>>
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