On Tue, Dec 21, 2010 at 08:20:14PM -0600, Alex Elder wrote: > On Tue, 2010-12-21 at 18:28 +1100, Dave Chinner wrote: > > From: Dave Chinner <dchinner@xxxxxxxxxx> > > > > To use the generic percpu counter infrastructure for counters that > > require conditional addition based on a threshold value we need > > special handling of the counter. Further, the caller needs to know > > the status of the conditional addition to determine what action to > > take depending on whether the addition occurred or not. Examples of > > this sort of usage are resource counters that cannot go below zero > > (e.g. filesystem free blocks). > > > > To allow XFS to replace it's complex roll-your-own per-cpu > > superblock counters, a single generic conditional function is > > required: percpu_counter_add_unless_lt(). This will add the amount > > to the counter unless the result would be less than the given > > threshold. A caller supplied threshold is required because XFS does > > not necessarily use the same threshold for every counter. > > > > percpu_counter_add_unless_lt() attempts to minimise counter lock > > traversals by only taking the counter lock when the threshold is > > within the error range of the current counter value. Hence when the > > threshold is not within the counter error range, the counter will > > still have the same scalability characteristics as the normal > > percpu_counter_add() function. > > > > Adding this functionality to the generic percpu counters allows us > > to remove the much more complex and less efficient XFS percpu > > counter code (~700 lines of code) and replace it with generic > > percpu counters. > > > > Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx> > > I want to look at this one more closely again in the > morning, but for now I'll just mention one nit, and > one easily fixed problem. > > -Alex > > . . . > > > + * Add @amount to @fdc if and only if result of addition is greater than or > ^^^ should be fbc > > > +EXPORT_SYMBOL(percpu_counter_add_unless_lt); > > + > > This has to be: > EXPORT_SYMBOL(__percpu_counter_add_unless_lt); > (with leading underscores). Yup, saw you comment about that on IRC overnight. Already fixed. ;) Cheers,, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
