> On Tue, 29 Jan 2008 16:49:02 +0100 > Miklos Szeredi <miklos@xxxxxxxxxx> wrote: > > > From: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> > > > > Provide a place in sysfs (/sys/class/bdi) for the backing_dev_info > > object. This allows us to see and set the various BDI specific > > variables. > > > > In particular this properly exposes the read-ahead window for all > > relevant users and /sys/block/<block>/queue/read_ahead_kb should be > > deprecated. > > This description is not complete. It implies that the readahead window is > not "properly" exposed for some "relevant" users. The reader is left > wondering what on earth this is referring to. I certainly don't know. > Perhaps when this information is revealed, we can work out what was > wrong with per-queue readahead tuning. I think Peter meant, that the readahead window was only exposed for block devices, and not things like NFS or FUSE. > > --- /dev/null 1970-01-01 00:00:00.000000000 +0000 > > +++ linux/Documentation/ABI/testing/sysfs-class-bdi 2008-01-29 13:02:46.000000000 +0100 > > @@ -0,0 +1,50 @@ > > +What: /sys/class/bdi/<bdi>/ > > +Date: January 2008 > > +Contact: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> > > +Description: > > + > > +Provide a place in sysfs for the backing_dev_info object. > > +This allows us to see and set the various BDI specific variables. > > + > > +The <bdi> identifyer can take the following forms: > > "identifier" Arrgh. Must run spellchecker on doc files :) > > +blk-NAME > > + > > + Block devices, NAME is 'sda', 'loop0', etc... > > But if I've done `mknod /dev/pizza-party 8 0', I'm looking for > blk-pizza-party, not blk-sda. > > But I might still have /dev/sda, too. An alternative would be to uniformly use MAJOR:MINOR in there. It would work for block devices and anonymous devices (NFS/FUSE) as well. Would that be any better? > > > +FSTYPE-MAJOR:MINOR > > + > > + Non-block device backed filesystems which provide their own > > + BDI, such as NFS and FUSE. MAJOR:MINOR is the value of st_dev > > + for files on this filesystem. > > + > > +default > > + > > + The default backing dev, used for non-block device backed > > + filesystems which do not provide their own BDI. > > + > > +Files under /sys/class/bdi/<bdi>/ > > +--------------------------------- > > + > > +read_ahead_kb (read-write) > > + > > + Size of the read-ahead window in kilobytes > > + > > +reclaimable_kb (read-only) > > + > > + Reclaimable (dirty or unstable) memory destined for writeback > > + to this device > > + > > +writeback_kb (read-only) > > + > > + Memory currently under writeback to this device > > + > > +dirty_kb (read-only) > > + > > + Global threshold for reclaimable + writeback memory > > + > > +bdi_dirty_kb (read-only) > > + > > + Current threshold on this BDI for reclaimable + writeback > > + memory > > + > > I dunno. A number of the things which you're exposing are closely tied to > present-day kernel implementation and may be irrelevant or even > unimplementable in a few years' time. Which ones? They could possibly be moved to debugfs, or something. I agree, that sysfs should be relatively stable. Thanks, Miklos - 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
