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.
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.
Signed-off-by: Timur Tabi <timur@freescale.com>
---
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 bdd5c43..2b685eb 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1736,6 +1736,59 @@ void free_pages(unsigned long addr, unsigned int order)
EXPORT_SYMBOL(free_pages);
+/**
+ * Allocate an exact number of pages of physically-contiguous memory.
+ *
+ * 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);
+
+/**
+ * Releases memory allocated via alloc_pages_exact()
+ *
+ * Release the memory allocated by a previous call to alloc_pages_exact.
+ *
+ * The first parameter must be the value returned by alloc_pages_exact(),
+ * and the 'size' parameter must be the same as was passed 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
--
