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

Michal Hocko
2020-10-02T07:11:29Z

On Thu 01-10-20 21:26:26, Uladzislau Rezki wrote:
> >
> > No, I meant going back to idea of new gfp flag, but adjust the implementation in
> > the allocator (different from what you posted in previous version) so that it
> > only looks at the flag after it tries to allocate from pcplist and finds out
> > it's empty. So, no inventing of new page allocator entry points or checks such
> > as the one you wrote above, but adding the new gfp flag in a way that it doesn't
> > affect existing fast paths.
> >
> OK. Now i see. Please have a look below at the patch, so we fully understand
> each other. If that is something that is close to your view or not:
>
> <snip>
> t a/include/linux/gfp.h b/include/linux/gfp.h
> index c603237e006c..7e613560a502 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -39,8 +39,9 @@ struct vm_area_struct;
> #define ___GFP_HARDWALL 0x100000u
> #define ___GFP_THISNODE 0x200000u
> #define ___GFP_ACCOUNT 0x400000u
> +#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. Besides that we certainly do not want to allow craziness like
__GFP_NO_LOCK | __GFP_RECLAIM (and similar), do we?
--
Michal Hocko
SUSE Labs