On 06/27/2018 09:54 AM, Michal Hocko wrote: > On Wed 27-06-18 09:50:01, Vlastimil Babka wrote: >> On 06/27/2018 09:34 AM, Michal Hocko wrote: >>> On Tue 26-06-18 10:04:16, Andrew Morton wrote: >>> >>> And as I've argued before the code would be wrong regardless. We would >>> leak the memory or worse touch somebody's else kmap without knowing >>> that. So we have a choice between a mem leak, data corruption k or a >>> silent fixup. I would prefer the last option. And blowing up on a BUG >>> is not much better on something that is easily fixable. I am not really >>> convinced that & ~__GFP_HIGHMEM is something to lose sleep over. >> >> Maybe put the fixup into a "#ifdef CONFIG_HIGHMEM" block and then modern >> systems won't care? In that case it could even be if (WARN_ON_ONCE(...)) >> so future cases with wrong expectations would become known. > > Yes that could be done as well. Or maybe we can make __GFP_HIGHMEM 0 for > !HIGHMEM systems. Does something really rely on it being non-zero? I guess gfp_zone() would have to be checked, dunno about the rewrite of GFP_ZONE_TABLE (CCing people). In general checks like "if (flags & __GFP_HIGHMEM)" would become false, which probably should not be a problem, unless something expect the flag to be there and errors out if it isn't.
