On Wed, Apr 05, 2017 at 03:10:58PM +0800, Huang, Ying wrote: > In general, kmalloc() will have less memory fragmentation than > vmalloc(). From Dave Hansen: For example, we have a two-page data > structure. vmalloc() takes two effectively random order-0 pages, > probably from two different 2M pages and pins them. That "kills" two > 2M pages. kmalloc(), allocating two *contiguous* pages, is very > unlikely to cross a 2M boundary (it theoretically could). That means > it will only "kill" the possibility of a single 2M page. More 2M > pages == less fragmentation. Wait, what? How does kmalloc() manage to allocate two pages that cross a 2MB boundary? AFAIK if you ask kmalloc to allocate N pages, it asks the page allocator for an order-log(N) page allocation. Being a buddy allocator, that comes back with an aligned set of pages. There's no way it can get the last page from a 2MB region and the first page from the next 2MB region. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
