On Thu, Apr 30, 2020 at 10:46:17AM +0200, Peter Zijlstra wrote: > On Wed, Apr 29, 2020 at 06:04:05PM -0700, Michel Lespinasse wrote:
> > - Have you considered passing a cmp() function to rb_add() and > > rb_add_cached(), and having these test cmp() < 0 rather than less() ? > > I figure every user will need to have a cmp() function, so it'd be > > nicer if they didn't also need a less() function, if the generated > > code is similar (if you checked and rejected it because of bad code, > > please just say so). > > I did consider it; in fact I my original helpers had that. > > The reaosn I went with less() over cmp() is that the add() vs find() > function signatures: > > bool (*less)(struct rb_node *, const struct rb_node *); > int (*cmp)(const void *, const struct rb_node *); > > differ anyway in the left-hand argument; this is 'fixable' when you > use an (on-stack) dummy object for find (as uprobes does), but that > doesn't always work, esp. when the object is big. And given you need two > functions anyway, I figured it was useful to name them differently. > > If you've looked at the other patches a bit, you'll see I've implemented > both functions as 'trivial' wrappers around a single compare function in > many cases. I just realized I'd already done all this at some point ;-) See rbtree_latch.h. Clearly I failed to realize the full potential back when I did that.
