Alexander Duyck <alexander.du...@gmail.com> writes:
> 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.
Note that this is on a should-never-happen error path, so there's no
need to be counting cycles.
--
Måns Rullgård
m...@mansr.com
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