On Wed, Oct 29, 2014 at 11:23:38AM -0700, Jason B. Akers wrote: > The following series enables the use of Solid State hybrid drives > ATA standard 3.2 defines the hybrid information feature, which provides a > means for the host driver to provide hints to the SSHDs to guide what to > place on the SSD/NAND portion and what to place on the magnetic media. > > This implementation allows user space applications to provide the cache hints > to the kernel using the existing ionice syscall. > > An application can pass a priority number coding up bits 11, 12, and 15 of > the ionice command to form a 3 bit field that encodes the following > priorities: > OPRIO_ADV_NONE, > IOPRIO_ADV_EVICT, /* actively discard cached data */ > IOPRIO_ADV_DONTNEED, /* caching this data has little value */ > IOPRIO_ADV_NORMAL, /* best-effort cache priority (default) */ > IOPRIO_ADV_RESERVED1, /* reserved for future use */ > IOPRIO_ADV_RESERVED2, > IOPRIO_ADV_RESERVED3, > IOPRIO_ADV_WILLNEED, /* high temporal locality */ > > For example the following commands from the user space will make dd IOs to be > generated with a hint of IOPRIO_ADV_DONTNEED assuming the SSHD is /dev/sdc. > > ionice -c2 -n4096 dd if=/dev/zero of=/dev/sdc bs=1M count=1024 > ionice -c2 -n4096 dd if=/dev/sdc of=/dev/null bs=1M count=1024
This looks to be the wrong way to implement per-IO priority information. How does a filesystem make use of this to make sure it's metadata ends up with IOPRIO_ADV_WILLNEED to store frequently accessed metadata in flash. Conversely, journal writes need to be issued with IOPRIO_ADV_DONTNEED so they don't unneceessarily consume flash space as they are never-read IOs... Cheers, Dave. -- Dave Chinner da...@fromorbit.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
