On Fri, Nov 21, 2014 at 06:48:49AM +0000, Minchan Kim wrote: > On Fri, Nov 21, 2014 at 01:33:26PM +0800, Ganesh Mahendran wrote: > > Hello > > > > 2014-11-21 11:54 GMT+08:00 Minchan Kim <minchan@xxxxxxxxxx>: > > > On Thu, Nov 20, 2014 at 09:21:56PM +0800, Mahendran Ganesh wrote: > > >> ZS_SIZE_CLASSES is calc by: > > >> ((ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE) / ZS_SIZE_CLASS_DELTA + 1) > > >> > > >> So when i is in [0, ZS_SIZE_CLASSES - 1), the size: > > >> size = ZS_MIN_ALLOC_SIZE + i * ZS_SIZE_CLASS_DELTA > > >> will not be greater than ZS_MAX_ALLOC_SIZE > > >> > > >> This patch removes the unnecessary check. > > > > > > It depends on ZS_MIN_ALLOC_SIZE. > > > For example, we would change min to 8 but MAX is still 4096. > > > ZS_SIZE_CLASSES is (4096 - 8) / 16 + 1 = 256 so 8 + 255 * 16 = 4088, > > > which exceeds the max. > > Here, 4088 is less than MAX(4096). > > > > ZS_SIZE_CLASSES = (MAX - MIN) / Delta + 1 > > So, I think the value of > > MIN + (ZS_SIZE_CLASSES - 1) * Delta = > > MIN + ((MAX - MIN) / Delta) * Delta = > > MAX > > will not exceed the MAX > > You're right. It was complext math for me. > I should go back to elementary school. > > Thanks! > > Acked-by: Minchan Kim <minchan@xxxxxxxxxx> I catch a nasty cold but above my poor math makes me think more. ZS_SIZE_CLASSES is broken. In above my example, current code cannot allocate 4096 size class so we should correct ZS_SIZE_CLASSES at first. zs_size_classes = zs_max - zs_min / delta + 1; if ((zs_max - zs_min) % delta) zs_size_classes += 1; Then, we need to code piece you removed. As well, we need to fix below. - area->vm_buf = (char *)__get_free_page(GFP_KERNEL); + area->vm_buf = kmalloc(ZS_MAX_ALLOC_SIZE); Hope I am sane in this time :( -- 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>