From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 24 Jun 2008 13:57:50 -0700 From: Andrew Morton Subject: Fw: [PATCH] Add alloc_pages_exact() and free_pages_exact() Message-Id: <20080624135750.0c59c6b9.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: linux-mm@kvack.org Cc: Timur Tabi List-ID: I'm applying this. Begin forwarded message: Date: Tue, 24 Jun 2008 11:40:49 -0500 From: Timur Tabi To: linux-kernel@vger.kernel.org, andi@firstfloor.org, randy.dunlap@oracle.com, corbet@lwn.net, torvalds@linux-foundation.org Subject: [PATCH] Add alloc_pages_exact() and free_pages_exact() alloc_pages_exact() is similar to alloc_pages(), except that it allocates the minimum number of pages to fulfill the request. This is useful if you want to allocate a very large buffer that is slightly larger than an even power-of-two number of pages. In that case, alloc_pages() will waste a lot of memory. Signed-off-by: Timur Tabi --- I have a video driver that wants to allocate a 5MB buffer. alloc_pages() will waste 3MB of physically-contiguous memory. Therefore, I would like to see alloc_pages_exact() added to 2.6.27. Please note that I am not a Linux VM expert. I wrote these functions based on guidance from Andi Kleen. I have no familiarity with NUMA, so I don't know how to handle that. Any and all suggestions are welcome. include/linux/gfp.h | 3 ++ mm/page_alloc.c | 53 +++++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 56 insertions(+), 0 deletions(-) diff --git a/include/linux/gfp.h b/include/linux/gfp.h index b414be3..1054801 100644 --- a/include/linux/gfp.h +++ b/include/linux/gfp.h @@ -215,6 +215,9 @@ extern struct page *alloc_page_vma(gfp_t gfp_mask, extern unsigned long __get_free_pages(gfp_t gfp_mask, unsigned int order); extern unsigned long get_zeroed_page(gfp_t gfp_mask); +void *alloc_pages_exact(size_t size, gfp_t gfp_mask); +void free_pages_exact(void *virt, size_t size); + #define __get_free_page(gfp_mask) \ __get_free_pages((gfp_mask),0) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 2f55295..08bf9d7 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1711,6 +1711,59 @@ void free_pages(unsigned long addr, unsigned int order) EXPORT_SYMBOL(free_pages); +/** + * alloc_pages_exact - allocate an exact number physically-contiguous pages. + * @size: the number of bytes to allocate + * @gfp_mask: GFP flags for the allocation + * + * This function is similar to alloc_pages(), except that it allocates the + * minimum number of pages to satisfy the request. alloc_pages() can only + * allocate memory in power-of-two pages. + * + * This function is also limited by MAX_ORDER. + * + * Memory allocated by this function must be released by free_pages_exact(). + */ +void *alloc_pages_exact(size_t size, gfp_t gfp_mask) +{ + unsigned int order = get_order(size); + unsigned long addr; + + addr = __get_free_pages(gfp_mask, order); + if (addr) { + unsigned long alloc_end = addr + (PAGE_SIZE << order); + unsigned long used = addr + PAGE_ALIGN(size); + + split_page(virt_to_page(addr), order); + while (used < alloc_end) { + free_page(used); + used += PAGE_SIZE; + } + } + + return (void *)addr; +} +EXPORT_SYMBOL(alloc_pages_exact); + +/** + * free_pages_exact - release memory allocated via alloc_pages_exact() + * @virt: the value returned by alloc_pages_exact. + * @size: size of allocation, same value as passed to alloc_pages_exact(). + * + * Release the memory allocated by a previous call to alloc_pages_exact. + */ +void free_pages_exact(void *virt, size_t size) +{ + unsigned long addr = (unsigned long)virt; + unsigned long end = addr + PAGE_ALIGN(size); + + while (addr < end) { + free_page(addr); + addr += PAGE_SIZE; + } +} +EXPORT_SYMBOL(free_pages_exact); + static unsigned int nr_free_zone_pages(int offset) { struct zoneref *z; -- 1.5.5 -- 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/ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org