11 Apr
2014
11 Apr
'14
12:22 a.m.
Hi
On Thu, Apr 10, 2014 at 11:33 PM, Tony Battersby tonyb@cybernetics.com wrote:
For O_DIRECT the kernel pins the submitted pages in memory for DMA by incrementing the page reference counts when the I/O is submitted, allowing the pages to be modified by DMA even if they are no longer mapped in the address space of the process. This is different from a regular read(), which uses the CPU to copy the data and will fail if the pages are not mapped.
Can you please provide an example code-path? For instance, file_read_actor() does not pin any pages but only keeps the user-space address and resolves it once it has data to write.
Thanks David