On 10/12/2016 02:53 PM, Michal Hocko wrote: > On Wed 12-10-16 08:28:17, zijun_hu wrote: >> On 2016/10/12 1:22, Michal Hocko wrote: >>> On Tue 11-10-16 21:24:50, zijun_hu wrote: >>>> From: zijun_hu <zijun_hu@xxxxxxx> >>>> >>>> the LSB of a chunk->map element is used for free/in-use flag of a area >>>> and the other bits for offset, the sufficient and necessary condition of >>>> this usage is that both size and alignment of a area must be even numbers >>>> however, pcpu_alloc() doesn't force its @align parameter a even number >>>> explicitly, so a odd @align maybe causes a series of errors, see below >>>> example for concrete descriptions. >>> >>> Is or was there any user who would use a different than even (or power of 2) >>> alighment? If not is this really worth handling? >>> >> >> it seems only a power of 2 alignment except 1 can make sure it work very well, >> that is a strict limit, maybe this more strict limit should be checked > > I fail to see how any other alignment would actually make any sense > what so ever. Look, I am not a maintainer of this code but adding a new > code to catch something that doesn't make any sense sounds dubious at > best to me. > > I could understand this patch if you see a problem and want to prevent > it from repeating bug doing these kind of changes just in case sounds > like a bad idea. > thanks for your reply should we have a generic discussion whether such patches which considers many boundary or rare conditions are necessary. should we make below declarations as conventions 1) when we say 'alignment', it means align to a power of 2 value for example, aligning value @v to @b implicit @v is power of 2 , align 10 to 4 is 12 2) when we say 'round value @v up/down to boundary @b', it means the result is a times of @b, it don't requires @b is a power of 2 -- 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>