On Thu, Aug 06, 2015 at 10:52:47AM +0300, Boaz Harrosh wrote: > On 08/06/2015 06:24 AM, Dave Chinner wrote: > > On Wed, Aug 05, 2015 at 09:42:54PM -0400, Linda Knippers wrote: > >> On 08/05/2015 06:01 PM, Dave Chinner wrote: > >>> On Wed, Aug 05, 2015 at 04:19:08PM -0400, Jeff Moyer wrote: > <> > >>>> > >>>> I sat down with Linda to look into it, and the problem is that mkfs.xfs > >>>> sets the blocksize of the device to 512 (via BLKBSZSET), and then reads > >>>> from the last sector of the device. This results in dax_io trying to do > >>>> a page-sized I/O at 512 bytes from the end of the device. > >>> > > This part I do not understand. how is mkfs.xfs reading the sector? > Is it through open(/dev/pmem0,...) ? O_DIRECT? mkfs.xfs uses O_DIRECT. Only if open(O_DIRECT) fails or mkfs.xfs is told that it is working on an image file does it fall back to buffered IO. All of the XFS userspace tools work this way to prevent page cache pollution issues with read-once or write-once data during operation. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
