Re: Does get_user_pages_fast lock the user pages in memory in my case?

[Huang Shijie <shijie8@gmail.com>]

KOSAKI Motohiro a??e??:
>> http://v4l2spec.bytesex.org/spec/r13696.htm
>> shows the vidioc_reqbufs(). It determines the method of IO : "Memory 
>> Mapping or User Pointer I/O"
>>
>> The application developers can support any methodes of the Two, there is 
>> no mandatory request to realize
>> both methods.   For example, the Mplayer only support the "memory 
>> maping" method ,and it does't support the "user pointer",
>> while the VLC supports both.
>>     
>
> I greped VIDIOC_REQBUFS on current tree.
> Almost driver has following check.
>
>         if (rb->memory != V4L2_MEMORY_MMAP)
> 		return -EINVAL;
>
> IOW, almost one don't provide V4L2_MEMORY_USERPTR method.
> Thus, I think any userland application don't want use V4L2_MEMORY_USERPTR.
> I recommend you also return -EINVAL.
>
>   
Thanks.

In the V4L2_MEMORY_USERPTR method, what I want to do is pin the 
anonymous pages in memory.

I used to add the VM_LOCKED to vma associated with the pages.In my 
opinion, the pages will:
LRU_ACTIVE_ANON ---> LRU_INACTIVE_ANON---> LRU_UNEVICTABLE

so the pages are pinned in memory.It was ugly, but it works I think.
Do you have any suggestions about this method?





> I think we can't implement V4L2_MEMORY_USERPTR properly.
> it is mistake by specification.
>
>
>
>
>
>   

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>