Messages in this thread | | | Date | Mon, 1 Jan 2007 03:33:47 -0500 (EST) | From | "Robert P. J. Day" <> | Subject | Re: replace "memset(...,0,PAGE_SIZE)" calls with "clear_page()"? |
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On Mon, 1 Jan 2007, Folkert van Heusden wrote:
> > > regarding alignment that don't allow clear_page() to be used > > > copy_page() in the memcpy() case), but it's going to need a lot of > > Maybe these optimalisations should be in the coding style docs?
i was thinking of submitting the following as a new "chapter" for the doc -- it would address *some* of these issues:
Chapter XX: Page-related memory management
The following functions and macro definitions are available via include/linux/gfp.h for page-based memory management:
struct page *alloc_pages(gfp_mask, order); unsigned long __get_free_pages(gfp_mask, order); unsigned long get_zeroed_page(gfp_mask); void __free_pages(struct page *page, order); void free_pages(unsigned long addr, order);
#define alloc_page(gfp_mask) alloc_pages(gfp_mask, 0) #define __get_free_page(gfp_mask) __get_free_pages((gfp_mask),0) #define __free_page(page) __free_pages((page), 0) #define free_page(addr) free_pages((addr),0)
#define __get_dma_pages(gfp_mask, order) \ __get_free_pages((gfp_mask) | GFP_DMA,(order))
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.
(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 */
(d) If you need to clear (zero) a page, be aware that every architecture defines a clear_page() routine, either as a macro in include/<arch>/page.h or as an assembler routine.
You should check if it's appropriate to use that routine/macro, rather than making an explicit call to memset(...,0, PAGE_SIZE). - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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