On Mon, 29 Jun 2020, Matthew Wilcox wrote: > Sounds like we need a test somewhere that checks this behaviour. > > > In order to make such allocations possible one would have to create yet > > another kmalloc array for high memory. > > Not for this case because it goes straight to kmalloc_order(). What does > make this particular case impossible is that we can't kmap() a compound > page. We could vmap it, but why are we bothering?
Well yes it will work if the slab allocator falls back to the page allocator. Higher order allocation through kmalloc ;-). How much fun and uselessness .... Why not call the page allocator directly and play with all the bits you want? Any regular small object allocation with GFP_HIGH will lead to strange effects if the bit is not checked.
