Hi On Thu, Apr 10, 2014 at 11:33 PM, Tony Battersby <tonyb@xxxxxxxxxxxxxxx> 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>