On Wed, Nov 25, 2015 at 5:04 AM, Måns Rullgård <m...@mansr.com> wrote:
> Mason <slash....@free.fr> writes:
>
>> On 25/11/2015 13:45, Måns Rullgård wrote:
>>
>>> Mason wrote:
>>>
>>>> On 19/11/2015 14:02, Mans Rullgard wrote:
>>>>
>>>>> + if (dma_mapping_error(&dev->dev, dma_addr)) {
>>>>> + skb_free_frag(data);
>>>>> + return -ENOMEM;
>>>>> + }
>>>>
>>>> I'm back-porting this driver to 4.1
>>>>
>>>> skb_free_frag() was introduced in 4.2 by 181edb2bfa22b IIUC.
>>>>
>>>> +static inline void skb_free_frag(void *addr)
>>>> +{
>>>> + __free_page_frag(addr);
>>>> +}
>>>>
>>>> Should I just copy the definition of __free_page_frag() ?
>>>
>>> Looks like it ought to work. Try and find out. Not that you'll ever
>>> hit that error condition unless you fake it.
>>
>> Turns out __free_pages_ok() is static and I'd rather not touch
>> mm/page_alloc.c in my back-port.
>>
>> Since you say the error condition is rare, I think I'll go with
>> the code that 181edb2bfa22b replaced (put_page, IIUC).
>>
>> #include <linux/version.h>
>> #if LINUX_VERSION_CODE < KERNEL_VERSION(4,2,0)
>> #define skb_free_frag(data) put_page(virt_to_head_page(data))
>> #else
>> #error DELETE ME NOW (see commit 181edb2bfa22b)
>> #endif
>
> You can simply put_page(page) instead since we already have the
> virt_to_head_page() a few lines up.
What you could do is use __free_pages instead of __free_pages_ok.
Generally you will want to use __free_pages instead of put_page just
to avoid a bunch of unnecessary tests and function pointer accesses.
The result would look something like:
static inline void skb_free_frag(void *addr)
{
struct page *page = virt_to_head_page(addr);
__free_pages(page, compound_order(page));
}
Hope that helps.
- Alex
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