On Tue, Aug 28, 2018 at 03:27:27PM -0700, Matthew Wilcox wrote: > I find myself caught between two traditions. > > On the one hand, the radix tree has been calling the page cache dirty & > writeback bits "tags" for over a decade. > > On the other hand, using some of the bits _in a pointer_ as a tag has been > common practice since at least the 1960s. > https://en.wikipedia.org/wiki/Tagged_pointer and > https://en.wikipedia.org/wiki/31-bit > > EROFS wants to use tagged pointers in the radix tree / xarray. Right now, > they're building them by hand, which is predictably grotty-looking. > I think it's reasonable to provide this functionality as part of the > XArray API, _but_ it's confusing to have two different things called tags. > > I've done my best to document my way around this, but if we want to rename > the things that the radix tree called tags to avoid the problem entirely, > now is the time to do it. Anybody got a Good Idea? I have two ideas now. First, we could rename radix tree tags to xarray marks. That is, xa_mark_t xa_set_mark() xas_clear_mark() xas_for_each_marked() { } xa_marked() etc Second, we could call the tagged pointers typed pointers. That is, void *xa_mk_type(void *p, unsigned int type); void *xa_to_ptr(void *entry); int xa_ptr_type(void *entry); Any better ideas, or violent revulsion to either of the above ideas?
