On Fri, 2006-04-21 at 11:24 -0700, Zach Brown wrote:
> > the pointers are always going to be aligned. So let's just use the
> > lowest bit of the parent pointer instead. This shrinks the rb_node from
> > 4 machine-words to 3.
>
> We've seen this patch before, haven't we? :) I still like it.
Maybe. I thought I'd actually done it once before, but I couldn't
actually find it when I went looking. It should save about 40KiB of RAM
on my Nokia 770, because I should get 145 jffs2_node_frag objects in
each slab page instead of only 127 -- so yes, I like it too :)
> > Another pair of eyes on the 'remove dead code in rb_erase()' bit in
> > particular would be appreciated.
>
> I'll trade you some eyes for a description beyond the four words
> obvious, remove, dead, and code.
Plenty more words in the git commit. They don't make much sense without
the patch right below them, and you can see them in juxtaposition at
http://git.infradead.org/?p=users/dwmw2/rbtree-2.6.git;a=commitdiff;h=1975e59375756da4ff4e6e7d12f67485e813ace0
> > #define RB_RED 0
> > #define RB_BLACK 1
>
> > +#define rb_colour(r) ((r)->rb_parent_colour & 1)
>
> This creates a pretty strong bond between the two.. maybe a
> RB_COLOUR_MASK and use that and the _RED/_BLACK defines instead of the
> raw constants?
I think it's be better just to drop the RB_RED and RB_BLACK definitions.
> > +static inline void rb_set_parent(struct rb_node *rb, struct rb_node *p)
> > +{
>
> BUG_ON((unsigned long)p & 3);
Yeah, I suppose we could.
> > @@ -131,8 +147,7 @@ extern void rb_replace_node(struct rb_no
> > static inline void rb_link_node(struct rb_node * node, struct rb_node * parent,
> > struct rb_node ** rb_link)
> > {
> > - node->rb_parent = parent;
> > - node->rb_color = RB_RED;
> > + node->rb_parent_colour = (unsigned long )parent;
>
> use rb_set_parent(node, parent) and get the assertion.
Que?
--
dwmw2
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