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Message-ID: <84144f020603192325h54fd3212l1f4846fd40b9f074@mail.gmail.com>
Date: Mon, 20 Mar 2006 09:25:06 +0200
From: "Pekka Enberg" <penberg@cs.helsinki.fi>
To: "Oliver Neukum" <oliver@neukum.org>
Subject: Re: [PATCH]use kzalloc in vfs where appropriate
Cc: "Arjan van de Ven" <arjan@infradead.org>,
       "Matthew Wilcox" <matthew@wil.cx>, viro@zeniv.linux.org.uk,
       linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
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	 <200603191429.21776.oliver@neukum.org>
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Hi Oliver,

On 3/19/06, Oliver Neukum <oliver@neukum.org> wrote:
> Yes it is. The generated code is identical. But on second thought this is still
> not optimal. A full division is generated:
>
>         xorl    %edx, %edx
>         movl    $2147483647, %eax
>         movq    $0, 40(%rsp)
>         divq    %rcx
>         movl    $8, %edx
>         cmpq    %rax, %rdx
>         ja      .L313
>
> Rewriting the test as:
> n!=0 && n > INT_MAX / size
> saves the division because size is much likelier to be a constant, and indeed
> the code is better:
>
>         cmpq    $268435455, %rax
>         movq    $0, 40(%rsp)
>         ja      .L313
>
> Is there anything I am missing?

Did you check allyesconfig vmlinux size before and after? If it helps,
like it probably does, post a patch!

                                   Pekka
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