GFP_ATOMIC means roughly "make the allocation operation atomic". ThisRegards
means that the kernel will try to find the memory using a pile of free
memory set aside for urgent allocation. If that pile doesn't have
enough free pages, the operation will fail. This flag is useful for
allocation within interrupt handlers.
GFP_KERNEL will try a little harder to find memory. There's a
possibility that the call to kmalloc() will sleep while the kernel is
trying to find memory (thus making it unsuitable for interrupt
handlers). It's much more rare for an allocation with GFP_KERNEL to
fail than with GFP_ATOMIC.
In all cases, kmalloc() should only be used allocating small amounts of
memory (a few kb). vmalloc() is better for larger amounts.
sanjeev sharma
On Thu, Apr 2, 2009 at 8:49 PM, Peter Teoh <htmldeveloper@xxxxxxxxx> wrote:
On Thu, Apr 2, 2009 at 8:46 AM, Lal <learner.kernel@xxxxxxxxx> wrote:this is new to me, can i know why it should be GFP_ATOMIC?
> On Tue, Mar 31, 2009 at 2:03 PM, nidhi mittal <nidhimittal19@xxxxxxxxx> wrote:
>> hi
>> i have written a very simple ram based block device driver
>> processing request asynchronously
>>
>> wherein
>> in request function -- dequeue the req from req queue and add it to the
>> linked list
>> then in the function triggered by timer
>> handle each req from the linked list
>> then blk_end_requets is called upon completion of request .
>>
>>
>
>> blkdev_dequeue_request(req);
>> my_req = (struct filtered_request*)kzalloc(sizeof(struct
>> filtered_request),GFP_KERNEL);
>
> In request function, you should use GFP_ATOMIC
>
--
Regards,
Peter Teoh
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