Re: dm ioctl: Restore __GFP_HIGH in copy_params()

From: Michal Hocko
Date: Tue May 23 2017 - 02:05:43 EST

On Mon 22-05-17 13:35:41, David Rientjes wrote:
> On Mon, 22 May 2017, Mike Snitzer wrote:
> > While adding the __GFP_NOFAIL flag would serve to document expectations
> > I'm left unconvinced that the memory allocator will _not fail_ for an
> > order-0 page -- as Mikulas said most ioctls don't need more than 4K.
> __GFP_NOFAIL would make no sense in kvmalloc() calls, ever, it would never
> fallback to vmalloc :)

Sorry, I could have been more specific. You would have to opencode
kvmalloc obviously. It is documented to not support this flag for the
reasons you have mentioned above.

> I'm hoping this can get merged during the 4.12 window to fix the broken
> commit d224e9381897.

I obviously disagree. Relying on memory reserves for _correctness_ is
clearly broken by design, full stop. But it is dm code and you are going
it is responsibility of the respective maintainers to support this code.
Michal Hocko