Re: [PATCH] dma/pool: do not complain if DMA pool is not allocated

From: Christoph Hellwig <hch@lst.de>
To: Michal Hocko <mhocko@suse.com>
Cc: Christoph Hellwig <hch@lst.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Baoquan He <bhe@redhat.com>,
	John Donnelly <john.p.donnelly@oracle.com>,
	David Hildenbrand <david@redhat.com>,
	linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] dma/pool: do not complain if DMA pool is not allocated
Date: Thu, 11 Aug 2022 09:27:26 +0200	[thread overview]
Message-ID: <20220811072726.GA13886@lst.de> (raw)
In-Reply-To: <Yj3zyLs4f+ba6UqF@dhcp22.suse.cz>

On Fri, Mar 25, 2022 at 05:54:32PM +0100, Michal Hocko wrote:
> > > I thought there are only few pages in the managed by the DMA zone. This
> > > is still theoretically possible so I think __GFP_NOWARN makes sense here
> > > but it would require to change the patch description.
> > > 
> > > Is this really worth it?
> > 
> > In general I think for kernels where we need the pool and can't allocate
> > it, a warning is very useful.  We just shouldn't spew it when there is
> > no need for the pool to start with.
> 
> Well, do we have any way to find that out during early boot?

In general an architecture / configuration that selects
CONFIG_ZONE_DMA needs it.  We could try to reduce that dependency and/or
make it boot time configurable, but there's still plenty of device with
sub-32bit addessing limits around, so I'm not sure it would help much.