Re: [PATCH] slab: prevent warnings when allocating with __GFP_NOWARN

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 11 Jun 2013 18:16:08 +0300 Pekka Enberg <penberg@kernel.org> wrote:

> On Tue, 11 Jun 2013, Sasha Levin wrote:
> >> I think that leaving the warning makes sense to catch similar
> >> things which are actually bugs - we had a similar issue with
> >> /dev/kmsg (if I remember correctly) which actually pointed to
> >> a bug.
> 
> On 6/11/13 6:14 PM, Christoph Lameter wrote:
> > Right. Requesting an allocation larger than even supported by the page
> > allocator from the slab allocators that are specializing in allocations of
> > small objects is usually an indication of a problem in the code.
> 
> So you're OK with going forward with Sasha's patch?

Yes please.  slab should honour __GFP_NOWARN.

__GFP_NOWARN is frequently used by kernel code to probe for "how big an
allocation can I get".  That's a bit lame, but it's used on slow paths
and is pretty simple.

In the case of pipe_set_size(), it's userspace who is doing the
probing: an application can request a huge pipe buffer and if that
fails, try again with a smaller one.  It's just wrong to emit a kernel
warning in this case.  Plus, we've already reported the failure
anyway, by returning -ENOMEM from pipe_fcntl().

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