Messages in this thread | | | Subject | Re: [PATCH] Shrink rbtree | From | David Woodhouse <> | Date | Fri, 21 Apr 2006 20:06:52 +0100 |
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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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