Re: [Xen-devel] [PATCH v6 02/16 RESEND] rbtree: empty nodes have no color

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.11.17 at 16:19, <kpraveen.lkml@xxxxxxxxx> wrote:
> From: Michel Lespinasse <walken@xxxxxxxxxx>
> 
> Empty nodes have no color.  We can make use of this property to simplify
> the code emitted by the RB_EMPTY_NODE and RB_CLEAR_NODE macros.  Also,
> we can get rid of the rb_init_node function which had been introduced by
> commit 88d19cf37952 ("timers: Add rb_init_node() to allow for stack
> allocated rb nodes") to avoid some issue with the empty node's color not
> being initialized.
> 
> I'm not sure what the RB_EMPTY_NODE checks in rb_prev() / rb_next() are
> doing there, though.  axboe introduced them in commit 10fd48f2376d
> ("rbtree: fixed reversed RB_EMPTY_NODE and rb_next/prev").  The way I
> see it, the 'empty node' abstraction is only used by rbtree users to
> flag nodes that they haven't inserted in any rbtree, so asking the
> predecessor or successor of such nodes doesn't make any sense.
> 
> One final rb_init_node() caller was recently added in sysctl code to
> implement faster sysctl name lookups.  This code doesn't make use of
> RB_EMPTY_NODE at all, and from what I could see it only called
> rb_init_node() under the mistaken assumption that such initialization was
> required before node insertion.
> 
> [sfr@xxxxxxxxxxxxxxxx: fix net/ceph/osd_client.c build]
> Signed-off-by: Michel Lespinasse <walken@xxxxxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Acked-by: David Woodhouse <David.Woodhouse@xxxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> Cc: Daniel Santos <daniel.santos@xxxxxxxxx>
> Cc: Jens Axboe <axboe@xxxxxxxxx>
> Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
> Cc: John Stultz <john.stultz@xxxxxxxxxx>
> Signed-off-by: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> [Linux commit 4c199a93a2d36b277a9fd209a0f2793f8460a215]
> 
> Ported rbtree.h and rbtree.c changes which are relevant to Xen.
> 
> Signed-off-by: Praveen Kumar <kpraveen.lkml@xxxxxxxxx>

Acked-by: Jan Beulich <jbeulich@xxxxxxxx>



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