linux-kernel - Re: [PATCH] Remove initialization of page_table in one_page_table

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Message-ID: <alpine.DEB.2.00.0907140317001.22788@chino.kir.corp.google.com>
Date:	Tue, 14 Jul 2009 03:18:39 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Zhaolei <zhaolei@...fujitsu.com>
cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Remove initialization of page_table in
 one_page_table_init()

On Tue, 14 Jul 2009, Zhaolei wrote:

> diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
> index 3cd7711..55da09b 100644
> --- a/arch/x86/mm/init_32.c
> +++ b/arch/x86/mm/init_32.c
> @@ -108,13 +108,13 @@ static pmd_t * __init one_md_table_init(pgd_t *pgd)
> static pte_t * __init one_page_table_init(pmd_t *pmd)
> {
>     if (!(pmd_val(*pmd) & _PAGE_PRESENT)) {
> -        pte_t *page_table = NULL;
> +        pte_t *page_table;
> 
>         if (after_bootmem) {
> #if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_KMEMCHECK)
>             page_table = (pte_t *) alloc_bootmem_pages(PAGE_SIZE);
> -#endif
>             if (!page_table)
> +#endif
>                 page_table =
>                 (pte_t *)alloc_bootmem_low_pages(PAGE_SIZE);
>         } else

Nack, gcc will already optimize the branch out for configs without 
CONFIG_DEBUG_PAGEALLOC and CONFIG_KMEMCHECK.  The only thing this change 
does is make the code less readable.
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