On Mon, Aug 6, 2012 at 8:38 AM, Peter Zijlstra [off-list ref] wrote:

On Mon, 2012-08-06 at 16:17 +0200, Peter Zijlstra wrote:

quoted

Why would every user need to replicate the propagate and rotate
boilerplate?

So I don't have a tree near that any of this applies to (hence no actual
patch)

All right, here are instructions to get a tree this will apply to :)
1- fetch linux-next tree
2- check out next-20120806
3- revert e406c4110c968b7691c4ccfadcd866a74a72fa5b (was sent as
previous RFC version of this series, didn't realize it had made it
into -mm)
4- apply patches 1 and 3-9 of this series (patch 2 was also sent as
previous RFC version and made it into -mm)

but why can't we have something like:

struct rb_augment_callback {
        const bool (*update)(struct rb_node *node);
        const int offset;
        const int size;
};

#define RB_AUGMENT_CALLBACK(_update, _type, _rb_member, _aug_member)    \
(struct rb_augment_callback){                                           \
        .update = _update,                                              \
        .offset = offsetof(_type, _aug_member) -                        \
                  offsetof(_type, _rb_member),                          \
        .size   = sizeof(((_type *)NULL)->_aug_member),                 \
}

static __always_inline void
augment_copy(struct rb_node *dst, struct rb_node *src,
             const rb_augment_callback *ac)
{
        memcpy((void *)dst + ac->offset,
               (void *)src + ac->offset,
               ac->size);
}

static __always_inline void
augment_propagate(struct rb_node *rb, struct rb_node *stop,
                  const struct rb_augment_callback *ac)
{
        while (rb != stop) {
                if (!ac->update(rb))
                        break;
                rb = rb_parent(rb);
        }
}

static __always_inline void
augment_rotate(struct rb_node *old, struct rb_node *new.
               const struct rb_augment_callback *ac)
{
        augment_copy(new, old, ac);
        (void)ac->update(old);
}

I don't think this would work well, because ac->offset and ac->size
wouldn't be known at the point where they are needed, so the memcpy
wouldn't be nicely optimized into a fetch and store of the desired
size.

However, I wouldn't have a problem with declaring all 3 callbacks (and
the struct holding them) using a preprocessor macro as you propose.
Would that seem fine with you ? I can send an add-on patch to do that.

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.

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