[patch, 2.5] __vmalloc allocates spurious page?

From: Marcus Alanen (maalanen@ra.abo.fi)
Date: Tue Oct 15 2002 - 14:32:22 EST

Hi,

I think __vmalloc allocates an unnecessary page. While the virtual
address space should have a one-page hole in it, that is taken care of
by get_vm_area. All other routines (particularly map_vm_area)
subtract PAGE_SIZE from area->size before usage, so the last page
table entry isn't even set up.

The unnecessary page is allocated only if size is initially a multiple
of PAGE_SIZE, which sounds like a common case.

Marcus

diff -Naurd --exclude-from=/home/maalanen/linux/base/diff_exclude linus-2.5.42/mm/vmalloc.c msa-2.5.42/mm/vmalloc.c
--- linus-2.5.42/mm/vmalloc.c Sat Oct 12 16:42:57 2002
+++ msa-2.5.42/mm/vmalloc.c Tue Oct 15 21:53:10 2002
@@ -387,7 +387,7 @@
         if (!area)
                 return NULL;
 
- nr_pages = (size+PAGE_SIZE) >> PAGE_SHIFT;
+ nr_pages = (size+PAGE_SIZE-1) >> PAGE_SHIFT;
         array_size = (nr_pages * sizeof(struct page *));
 
         area->nr_pages = nr_pages; 

-- 
Marcus Alanen                       * Software Construction Laboratory *
marcus.alanen@abo.fi   * http://www.tucs.fi/Research/labs/softcons.php *

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