On Wed 28-08-24 18:58:43, Kent Overstreet wrote: > On Wed, Aug 28, 2024 at 09:26:44PM GMT, Michal Hocko wrote: > > On Wed 28-08-24 15:11:19, Kent Overstreet wrote: > > > On Wed, Aug 28, 2024 at 07:48:43PM GMT, Matthew Wilcox wrote: > > > > On Wed, Aug 28, 2024 at 10:06:36AM -0400, Kent Overstreet wrote: > > > > > vmalloc doesn't correctly respect gfp flags - gfp flags aren't used for > > > > > pte allocation, so doing vmalloc/kvmalloc allocations with reclaim > > > > > unsafe locks is a potential deadlock. > > > > > > > > Kent, the approach you've taken with this was NACKed. You merged it > > > > anyway (!). Now you're spreading this crap further, presumably in an effort > > > > to make it harder to remove. > > > > > > Excuse me? This is fixing a real issue which has been known for years. > > > > If you mean a lack of GFP_NOWAIT support in vmalloc then this is not a > > bug but a lack of feature. vmalloc has never promissed to support this > > allocation mode and a scoped gfp flag will not magically make it work > > because there is a sleeping lock involved in an allocation path in some > > cases. > > > > If you really need this feature to be added then you should clearly > > describe your usecase and listen to people who are familiar with the > > vmalloc internals rather than heavily pushing your direction which > > doesn't work anyway. > > Michal, I'm plenty familiar with the vmalloc internals. Given that you > didn't even seem to be aware of how it doesn't respect gfp flags, you > seem to be the person who hasn't been up to speed in this discussion. GFP_NOWAIT is explicitly documented as unsupported (__vmalloc_node_range_noprof). vmalloc internals are using vmap_purge_lock and blocking notifiers (vmap_notify_list) in rare cases so PF_MEMALLOC_NORECLAIM is not really sufficient to provide NOWAIT semantic (this is really not just about page tables allocations). There might be other places that require blocking - I do not claim to be an expert on the vmalloc allocator. Just my 2 cents do whatever you want with this information. It seems that this discussion is not going to be really productive so I will leave you here. If you reconsider and realize that a productive discussion realy requires also listening and respect then get back and we can try again. Good luck! -- Michal Hocko SUSE Labs
