Re: [RFC-PATCH 2/4] mm: Add __rcu_alloc_page_lockless() func.

[Peter Zijlstra]

On Thu, Sep 24, 2020 at 10:16:14AM +0200, Uladzislau Rezki wrote:
> Other option is if we had unconditionally enabled PREEMPT_COUNT config.
> It would be easy to identify a context type and invoke a page allocator
> if a context is preemtale. But as of now preemptable() is "half" working.
> Thomas uploaded patches to make it unconditional. But it can be blocked.

While I in principle support Thomas' patch, I think this is an abuse and
still complete wrong.

Not all preemptible() context can deal with GFP_KERNEL (GFP_NOFS
existing should be a clue). !preemptible context cannot unconditionally
deal with GFP_NOWAIT, consider using it while holding zone->lock.

The preemption context does not say antying much useful about the
allocation context.