linux-kernel - Re: replace "memset(...,0,PAGE_SIZE)" calls with "clear

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Date:	Sat, 30 Dec 2006 21:49:35 +0100
From:	Denis Vlasenko <vda.linux@...glemail.com>
To:	"Robert P. J. Day" <rpjday@...dspring.com>
Cc:	Linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: replace "memset(...,0,PAGE_SIZE)" calls with "clear_page()"?

On Friday 29 December 2006 07:16, Robert P. J. Day wrote:
> 
>   is there some reason there are so many calls of the form
> 
>   memset(addr, 0, PAGE_SIZE)
> 
> rather than the apparently equivalent invocation of
> 
>   clear_page(addr)
> 
> the majority of architectures appear to define the clear_page() macro
> in their include/<arch>/page.h header file, but not entirely
> identically, and in some cases that definition is conditional, as with
> i386:
> 
> =============================================================
> #ifdef CONFIG_X86_USE_3DNOW
> ...
> #define clear_page(page)        mmx_clear_page((void *)(page))
> ...
> #else
> ...
> #define clear_page(page)        memset((void *)(page), 0, PAGE_SIZE)
> ...
> #endif
> ============================================================
> 
>   should it perhaps be part of the CodingStyle doc to use the
> clear_page() macro rather than an explicit call to memset()?  (and
> should all architectures be required to define that macro?)

clear_page assumes that given address is page aligned, I think.
It may fail if you feed it with misaligned region's address.
--
vda
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