Re: [PATCH] block,blkcg: use __GFP_NOWARN for best-effort allocations in blkcg

[Tejun Heo]

Hello,

On Wed, Nov 23, 2016 at 09:50:12AM +0100, Vlastimil Babka wrote:
> > You'd certainly _hope_ that atomic allocations either have fallbacks
> > or are harmless if they fail, but I'd still rather see that
> > __GFP_NOWARN just to make that very much explicit.
> 
> A global change to GFP_NOWAIT would of course mean that we should audit its
> users (there don't seem to be many), whether they are using it consciously
> and should not rather be using GFP_ATOMIC.

A while ago, I thought about something like, say, GFP_MAYBE which is
combination of NOWAIT and NOWARN but couldn't really come up with
scenarios where one would want to use NOWAIT w/o NOWARN.  If an
allocation is important enough to warn the user of its failure, it
better be dipping into the atomic reserve pool; otherwise, it doesn't
make sense to make noise.

Maybe we can come up with a better name which signifies that this is
likely to fail every now and then but I still think it'd be beneficial
to make it quiet by default.  Linus, do you still think NOWARN should
be explicit?

Thanks.

-- 
tejun