On Thu 15-02-18 07:57:37, James Bottomley wrote: > On Thu, 2018-02-15 at 15:48 +0100, Michal Hocko wrote: > > On Wed 14-02-18 16:51:53, Goldwyn Rodrigues wrote: > > > > > > > > > Discussion with the memory folks towards scope based allocation > > > I am working on converting some of the GFP_NOFS memory allocation > > > calls to new scope API [1]. While other allocation types (noio, > > > nofs, noreclaim) are covered. Are there plans for identifying scope > > > of GFP_ATOMIC allocations? This should cover most (if not all) of > > > the allocation scope. > > > > There was no explicit request for that but I can see how some users > > might want it. I would have to double check but maybe this would > > allow vmalloc(GFP_ATOMIC). There were some users but most of them > > could have been changed in some way so the motivation is not very > > large. > > We have to be careful about that: most GFP_ATOMIC allocations are in > drivers and may be for DMA'able memory. We can't currently use vmalloc > memory for DMA to kernel via block because bio_map_kern() uses > virt_to_page() which assumes offset mapping. The latter is fixable, > obviously, but is it worth fixing? Very few GFP_ATOMIC allocations in > drivers will be for large chunks. Yes this might be not worth bothering. But from the conceptual POV GFP_ATOMIC resp. GFP_NOWAIT is very often a scope context - IRQs, preemption or RCU. So protecting all allocations from that context makes some sense. Not sure this is really worth spending another context bit though. -- Michal Hocko SUSE Labs
