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

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Message-Id: <1167572735.20929.750.camel@laptopd505.fenrus.org>
Date:	Sun, 31 Dec 2006 14:45:34 +0100
From:	Arjan van de Ven <arjan@...radead.org>
To:	Folkert van Heusden <folkert@...heusden.com>
Cc:	"Robert P. J. Day" <rpjday@...dspring.com>,
	Denis Vlasenko <vda.linux@...glemail.com>,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: replace "memset(...,0,PAGE_SIZE)" calls with "clear_page()"?

On Sun, 2006-12-31 at 14:39 +0100, Folkert van Heusden wrote:
> > > i don't see how that can be true, given that most of the definitions
> > > of the clear_page() macro are simply invocations of memset().  see for
> > > yourself:
> > *MOST*. Not all.
> > For example an SSE version will at least assume 16 byte alignment, etc
> > etc.
> 
> What about an if (adress & 15) { memset } else { sse stuff }
> or is that too obvious? :-)


it's only one example. clear_page() working only on a full page is a
nice restriction that allows the implementation to be optimized (again
the x86 hardware that had a hardware page zeroer comes to mind, the hw
is only 4 years old or so... and future hw may have it again)

clear_page() is more restricted than memset(). And that's good, it
allows for a more focused implementation. Otherwise there'd be no reason
to HAVE a clear_page(), if it just was a memset wrapper entirely.



-- 
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