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

From: Linus Torvalds
Date: Tue Nov 22 2016 - 17:14:08 EST

On Tue, Nov 22, 2016 at 8:48 AM, Tejun Heo <tj@xxxxxxxxxx> wrote:
> Hello,
> On Tue, Nov 22, 2016 at 04:47:49PM +0100, Vlastimil Babka wrote:
> > Thanks. Makes me wonder whether we should e.g. add __GFP_NOWARN to
> > GFP_NOWAIT globally at some point.
> Yeah, that makes sense. The caller is explicitly saying that it's
> okay to fail the allocation.

I'm not so convinced about the "atomic automatically means you shouldn't warn".

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.

Because as it is, atomic allocations certainly get to dig deeper into
our memory reserves, but they most definitely can fail, and I
definitely see how some code has no fallback because it thinks that
the deeper reserves mean that it will succeed.