Hi, Matthew, Matthew Wilcox <wi...@infradead.org> writes:
> 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. OK. I will change the comments in the next version. Best Regards, Huang, Ying
