linux-kernel - Re: [PATCH 2/2] radix-tree: Fix optimisation problem

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Message-ID: <CA+55aFxOJTOvxhv+hECHuGV+=xBHMuQitu86J=qBNmMYQ1ACSg@mail.gmail.com>
Date:   Sun, 25 Sep 2016 12:04:33 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Cedric Blancher <cedric.blancher@...il.com>
Cc:     Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Matthew Wilcox <mawilcox@...uxonhyperv.com>,
        Konstantin Khlebnikov <koct9i@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Matthew Wilcox <mawilcox@...rosoft.com>
Subject: Re: [PATCH 2/2] radix-tree: Fix optimisation problem

On Sun, Sep 25, 2016 at 11:04 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> The more I look at that particular piece of code, the less I like it. It's
> buggy shit. It needs to be rewritten entirely too actually check for sibling
> entries, not that ad-hoc arithmetic crap.

Here's my attempt at cleaning the mess up.

I'm not claiming it's perfect, but I think it's better. It gets rid of
the ad-hoc arithmetic in radix_tree_descend(), and just makes all that
be inside the is_sibling_entry() logic instead. Which got renamed and
made to actually return the main sibling. So now there is at least
only *one* piece of code that does that range comparison, and I don't
think there is any huge need to explain what's going on, because the
"magic" is unconditional.

Willy?

                 Linus

View attachment "patch.diff" of type "text/x-patch" (1766 bytes)