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

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Message-ID: <20241216222225.GF9803@noisy.programming.kicks-ass.net>
Date: Mon, 16 Dec 2024 23:22:25 +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 Tue, Dec 17, 2024 at 08:43:26AM +1030, Qu Wenruo wrote:
> 
> 
> 在 2024/12/13 19:36, Peter Zijlstra 写道:
> > On Thu, Dec 12, 2024 at 10:46:18AM -0600, Roger L. Beckermeyer III wrote:
> > > Adds rb_find_add_cached() as a helper function for use with
> > > red-black trees. Used in btrfs to reduce boilerplate code.
> > > 
> > > Suggested-by: Josef Bacik <josef@...icpanda.com>
> > > Signed-off-by: Roger L. Beckermeyer III <beckerlee3@...il.com>
> > 
> > Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> 
> I guess it's fine to merge this change through btrfs tree?

Yeah, I think so. I don't think there's anything else pending for this
file -- its not touched much.

> 
> Just curious about the existing cmp() and less() functions, as they only
> accept the exist node as const.
> 
> I'm wondering if this is intentional to allow the less/cmp() functions
> to modify the new node if needed.
> As I normally assume such cmp()/less() should never touch any node nor
> its entries.

Oh yeah, they probably should not. I think it's just because the
callchain as a whole does not have const on the new node (for obvious
raisins), and I failed to put it on for the comparators.

You could add it (and fix up the whole tree) and see if anything comes
apart.