linux-kernel - Re: [PATCH 1/6] rbtree: add rb_find_add

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20241213090507.GB21636@noisy.programming.kicks-ass.net>
Date: Fri, 13 Dec 2024 10:05:07 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Qu Wenruo <quwenruo.btrfs@....com>
Cc: "Roger L. Beckermeyer III" <beckerlee3@...il.com>, dsterba@...e.cz,
	oleg@...hat.com, mhiramat@...nel.org, linux-kernel@...r.kernel.org,
	josef@...icpanda.com, linux-btrfs@...r.kernel.org, lkp@...el.com
Subject: Re: [PATCH 1/6] rbtree: add rb_find_add_cached() to rbtree.h

On Fri, Dec 13, 2024 at 05:51:44PM +1030, Qu Wenruo wrote:
> 
> 
> 在 2024/12/13 03:16, Roger L. Beckermeyer III 写道:
> > Adds rb_find_add_cached() as a helper function for use with
> > red-black trees. Used in btrfs to reduce boilerplate code.
> 
> I won't call it boilerplate code though, it's just to utilize the cached
> rb tree feature as an optimization.

Nah, all this is boilerplate :-)

> > 
> > Suggested-by: Josef Bacik <josef@...icpanda.com>
> > Signed-off-by: Roger L. Beckermeyer III <beckerlee3@...il.com>
> > ---
> >   include/linux/rbtree.h | 37 +++++++++++++++++++++++++++++++++++++
> >   1 file changed, 37 insertions(+)
> > 
> > diff --git a/include/linux/rbtree.h b/include/linux/rbtree.h
> > index 7c173aa64e1e..0d4444c0cfb3 100644
> > --- a/include/linux/rbtree.h
> > +++ b/include/linux/rbtree.h
> > @@ -210,6 +210,43 @@ rb_add(struct rb_node *node, struct rb_root *tree,
> >   	rb_insert_color(node, tree);
> >   }
> > 
> > +/**
> > + * rb_find_add_cached() - find equivalent @node in @tree, or add @node
> > + * @node: node to look-for / insert
> > + * @tree: tree to search / modify
> > + * @cmp: operator defining the node order
> > + *
> > + * Returns the rb_node matching @node, or NULL when no match is found and @node
> > + * is inserted.
> > + */
> > +static __always_inline struct rb_node *
> > +rb_find_add_cached(struct rb_node *node, struct rb_root_cached *tree,
> > +	    int (*cmp)(struct rb_node *, const struct rb_node *))
> 
> This function is almost the same as rb_add_cached(), the only difference
> is the extra handling for the cmp function returning 0.
> 
> So I'm wondering if it's possible to enhance rb_add_cached(), or even
> refactor it so there can be a shared core function and rb_add_cached()
> and rb_find_add_cached() can reuse the same function.

Nope, rb_add_cached() can add multiple entries with the same key,
rb_find_add() cannot.

Also, note that all these things are effectively 'templates', they
generate code at the call site. The cmp() function as required for
find_add() is a tri-state return and generates more logic than the
binary less() required for add().