linux-kernel - Re: [PATCH v7 09/16] SUNRPC/cache: use new hashtable implementation

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Message-ID: <CA+55aFzO8DJJP3HBfgqXFac9r3=bYK+_nYe4cuXiNFg-623s6w@mail.gmail.com>
Date:	Mon, 29 Oct 2012 07:49:42 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	Sasha Levin <levinsasha928@...il.com>, tj@...nel.org,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
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Subject: Re: [PATCH v7 09/16] SUNRPC/cache: use new hashtable implementation

On Mon, Oct 29, 2012 at 5:42 AM, Mathieu Desnoyers
<mathieu.desnoyers@...icios.com> wrote:
>
> So defining e.g.:
>
> #include <linux/log2.h>
>
> #define DFR_HASH_BITS  (PAGE_SHIFT - ilog2(BITS_PER_LONG))
>
> would keep the intended behavior in all cases: use one page for the hash
> array.

Well, since that wasn't true before either because of the long-time
bug you point out, clearly the page size isn't all that important. I
think it's more important to have small and simple code, and "9" is
certainly that, compared to playing ilog2 games with not-so-obvious
things.

Because there's no reason to believe that '9' is in any way a worse
random number than something page-shift-related, is there? And getting
away from *previous* overly-complicated size calculations that had
been broken because they were too complicated and random, sounds like
a good idea.

            Linus
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