On Wed 09-12-15 15:07:50, Marc Gonzalez wrote: > On 09/12/2015 14:55, Michal Hocko wrote: > > On Tue 08-12-15 18:25:31, Sebastian Frias wrote: > >> Hi, > >> > >> We are porting a driver from Linux 3.4.39+ to 4.1.13+, CPU is Cortex-A9. > >> > >> The driver maps kmalloc'ed memory to user space. > > > > This sounds like a terrible idea to me. Why don't you simply use the > > page allocator directly? Try to imagine what would happen if you mmaped > > a kmalloc with a size which is not page aligned? mmaped memory uses > > whole page granularity. > > According to the source code, this kernel module calls > > kmalloc(1 << 17, GFP_KERNEL | __GFP_REPEAT); So I guess you are mapping with 32pages granularity? If this is really needed for internal usage you can use highorder page and map its subpages directly. > I suppose kmalloc() would return page-aligned memory? I do not think there is any guarantee like that. AFAIK you only get guarantee for the natural word alignment. Slab allocator is allowed to use larger allocation and put its metadata or whatever before the returned pointer. -- Michal Hocko SUSE Labs -- 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>