On Thu 2014-10-30 07:14:17, Dave Chinner wrote: > 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... Well, that makes sense, but we still want some kind of per-application priority. I'd like ~/.chromium directory cached in the SSD part, but I don't neccessarily want /data/backup directory cached in the SSD... Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
