linux-kernel - Re: [PATCH 1/9] rbtree: Cache leftmost node internally

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Date:   Sat, 15 Jul 2017 08:28:41 -0700
From:   Davidlohr Bueso <dave@...olabs.net>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     mingo@...nel.org, peterz@...radead.org, akpm@...ux-foundation.org,
        torvalds@...ux-foundation.org, jack@...e.cz,
        kirill.shutemov@...ux.intel.com, ldufour@...ux.vnet.ibm.com,
        mhocko@...e.com, mgorman@...hsingularity.net,
        linux-kernel@...r.kernel.org, Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH 1/9] rbtree: Cache leftmost node internally

On Sat, 15 Jul 2017, Christoph Hellwig wrote:

>Is the leftmost node so much more special than the rightmost one?
>
>Just asking because I have some code that caches both of them, but
>using your helpers would make it look very asymmetric..

Yeah, I thought of this, but ultimately decided that the leftmost
node was more used (rb_first vs rb_last calls) and probably not
worth adding the rightmost one which would endup enlarging the
structure even more.

That said, I do have some patches for the rbtree users to cache the
rightmost node, similarly to how it was done with the leftmost
before this patchset.

If folks don't mind enlarging rb_root_cached, I could definitely
add the rightmost, but it seems an overkill -- albeit asymmetric.

Thanks,
Davidlohr