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

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Date:	Mon, 01 Jan 2007 11:14:10 +0100
From:	Arjan van de Ven <arjan@...radead.org>
To:	"Robert P. J. Day" <rpjday@...dspring.com>
Cc:	Folkert van Heusden <folkert@...heusden.com>,
	Paul Mundt <lethal@...ux-sh.org>,
	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()"?


>   Given the above, some basic suggestions for page-based memory management:
> 
>  (a) If you need to allocate or free a single page, use the single page
>      version of the routine/macro, rather than calling the multi-page
>      version with an order value of zero, such as:
> 
> 	alloc_pages(gfp_mask, 0);	/* no */
> 	alloc_page(gfp_mask);		/* better */
> 
>  (b) If you need to allocate a single zeroed page by logical address,
>      use get_zeroed_page(), rather than __get_free_page() followed
>      by a call to memset() to clear that page.

both look good... I'd be in favor of this.
Maybe also add a part about using GFP_KERNEL whenever possible, GFP_NOFS
from filesystem writeout code and GFP_NOIO from block writeout code
(and never doing   in_interrupt()?GFP_ATOMIC:GFP_KERNEL !)


> 
>  (c) If you need to specifically allocate some DMA pages, use the
>      __get_dma_pages() macro, as in:
> 
> 	__get_free_pages(GFP_KERNEL|GFP_DMA, order)	/* no */
> 	__get_dma_pages(GFP_KERNEL, order)		/* better */

this.. does not really. GFP_DMA is an ancient artifact from the ISA
days. Better to describe the dma mapping interface (well give a pointer
to the doc that already exists about that), that one is REALLY for
allocating dma pages in this century.

-- 
if you want to mail me at work (you don't), use arjan (at) linux.intel.com
Test the interaction between Linux and your BIOS via http://www.linuxfirmwarekit.org

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