On Tue 05-01-16 15:26:02, Al Viro wrote: > On Tue, Jan 05, 2016 at 02:59:03PM +0100, Michal Hocko wrote: > > > > 3) vmalloc() is for large allocations. They will be page-aligned, > > > but *not* physically contiguous. OTOH, large physically contiguous > > > allocations are generally a bad idea. Unlike other allocators, there's > > > no variant that could be used in interrupt; freeing is possible there, > > > but allocation is not. Note that non-blocking variant *does* exist - > > > __vmalloc(size, GFP_ATOMIC, PAGE_KERNEL) can be used in atomic > > > contexts; it's the interrupt ones that are no-go. > > The last sentence I'd put into that part was complete crap... > > > It is also hardcoded GFP_KERNEL context so a usage from NOFS context > > needs a special treatment. > > ... in part because of this. GFP_ATOMIC __vmalloc() will be anything but, > and the only caller passing that is almost certainly bogus. Agreed as just replied in the other email thread which I have noticed only now. > As for NOFS/NOIO, > I wonder if we should apply that special treatment inside __vmalloc_area_node > rather than in callers; see the current thread on linux-mm for details... That would make a lot of sense to me. Spreading the _special_ treatment all over the kernel is certainly worse. > Another interesting issue is __GFP_HIGHMEM meaning for kmalloc and __vmalloc > resp. (should never be passed to kmalloc, should almost always be passed > to __vmalloc - the former needs pages mapped in kernel space, the latter > probably never needs a separate kernel alias for the data pages, to such > degree that I'm not sure if we shouldn't _force_ __GFP_HIGHMEM for data pages > allocation in __vmalloc_area_node()) I would have to think about this one some more. Let's not fragment the discussion and continue in that email thread: http://lkml.kernel.org/r/20160103071246.GK9938%40ZenIV.linux.org.uk -- Michal Hocko SUSE Labs -- 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>