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

Peter Zijlstra
2020-10-02T09:07:38Z

On Fri, Oct 02, 2020 at 09:50:14AM +0100, Mel Gorman wrote:
> On Fri, Oct 02, 2020 at 09:11:23AM +0200, Michal Hocko wrote:

> > > +#define ___GFP_NO_LOCKS 0x800000u
> >
> > Even if a new gfp flag gains a sufficient traction and support I am
> > _strongly_ opposed against consuming another flag for that. Bit space is
> > limited.
>
> That is definitely true. I'm not happy with the GFP flag at all, the
> comment is at best a damage limiting move. It still would be better for
> a memory pool to be reserved and sized for critical allocations.

This is one of the reasons I did a separate allocation function. No GFP
flag to leak into general usage.

> > Besides that we certainly do not want to allow craziness like
> > __GFP_NO_LOCK | __GFP_RECLAIM (and similar), do we?
>
> That would deserve to be taken to a dumpster and set on fire. The flag
> combination could be checked in the allocator but the allocator path fast
> paths are bad enough already.

Isn't that what we have CONFIG_DEBUG_VM for?