Hi On Thu, Apr 10, 2014 at 11:33 PM, Tony Battersby <tonyb at 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
