linux-kernel - Re: [RFC][PATCH] <linux/stringhash.h>: fix end_name

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Message-ID: <CA+55aFzyqjGXBjVmb+A7EUJr35a3BdZgYN29dD-KZXzY7k4e6Q@mail.gmail.com>
Date:   Mon, 5 Feb 2018 09:36:35 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Amir Goldstein <amir73il@...il.com>
Cc:     George Spelvin <linux@...encehorizons.net>,
        Al Viro <viro@...iv.linux.org.uk>,
        Miklos Szeredi <miklos@...redi.hu>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] <linux/stringhash.h>: fix end_name_hash() for 64bit long

On Mon, Feb 5, 2018 at 9:32 AM, Amir Goldstein <amir73il@...il.com> wrote:
>
> Assuming the fix is not moronic, I wouldn't even know where to begin testing
> its affects, or how to prove if there really is a problem.
> Any suggestions?

So I *think* that this was on purpose, but it's a long time ago, and
we've changed some of the hashing since.

And I think you're wrong that it's a no-op on 32-bit. It's a very
expensive and pointless multiplication there too, even if the *shift*
ends up being a nop-op.

The name hashing is pretty performance-sensitive.

                Linus