On Fri, Jul 30, 2010 at 06:32:04PM +0900, Minchan Kim wrote: > On Fri, Jul 30, 2010 at 5:55 AM, Dave Hansen <dave@xxxxxxxxxxxxxxxxxx> wrote: > > If you free up parts of the mem_map[] array, how does the buddy > > allocator still work? I thought we required at 'struct page's to be > > contiguous and present for at least 2^MAX_ORDER-1 pages in one go. (Dave, I don't seem to have your mail to reply to.) What you say is correct, and memory banks as a rule of thumb tend to be powers of two. We do have the ability to change MAX_ORDER (which we need to do for some platforms where there's only 1MB of DMA-able memory.) However, in the case of two 512KB banks, the buddy allocator won't try to satisfy a 1MB request as it'll only have two separate 2x512K free 'pages' to deal with, and 0x1M free 'pages'. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>