From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nick Piggin Subject: Re: Fw: [PATCH] Add alloc_pages_exact() and free_pages_exact() Date: Wed, 25 Jun 2008 11:39:50 +1000 References: <20080624135750.0c59c6b9.akpm@linux-foundation.org> In-Reply-To: <20080624135750.0c59c6b9.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200806251139.51142.nickpiggin@yahoo.com.au> Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton Cc: linux-mm@kvack.org, Timur Tabi List-ID: On Wednesday 25 June 2008 06:57, Andrew Morton wrote: > I'm applying this. Fine. And IIRC there are one or two places around the kernel that could be converted to use it. Why not just have a node id argument and call it alloc_pages_node_exact? so Christoph doesn't have to do it himself ;) Maybe you could also say that __GFP_COMPOUND cannot be used, and that the returned pages are "split" (work the same way as N indivudually allocated order-0 pages WRT refcounting). > 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; -- 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