Re: [PATCH v1] mm:free unused pages in kmalloc_order

[Christopher Lameter]

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.