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Date:   Thu, 24 Feb 2022 07:33:30 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Heiko Carstens <hca@linux.ibm.com>
Cc:     Christoph Hellwig <hch@lst.de>, Baoquan He <bhe@redhat.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
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        Halil Pasic <pasic@linux.ibm.com>,
        Vineeth Vijayan <vneethv@linux.ibm.com>
Subject: Re: [PATCH 00/22] Don't use kmalloc() with GFP_DMA
Message-ID: <20220224063330.GB20383@lst.de>
References: <20220219005221.634-1-bhe@redhat.com> <YhOaTsWUKO0SWsh7@osiris> <20220222084422.GA6139@lst.de> <YhaIcPmc8qi1zmnj@osiris>
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On Wed, Feb 23, 2022 at 08:18:08PM +0100, Heiko Carstens wrote:
> > The long term goal is to remove ZONE_DMA entirely at least for
> > architectures that only use the small 16MB ISA-style one.  It can
> > then be replaced with for example a CMA area and fall into a movable
> > zone.  I'd have to prototype this first and see how it applies to the
> > s390 case.  It might not be worth it and maybe we should replace
> > ZONE_DMA and ZONE_DMA32 with a ZONE_LIMITED for those use cases as
> > the amount covered tends to not be totally out of line for what we
> > built the zone infrastructure.
> 
> So probably I'm missing something; but for small systems where we
> would only have ZONE_DMA, how would a CMA area within this zone
> improve things?

It would not, but more importantly we would not need it at all.  The
thinking here is really about the nasty 16MB ISA-style zone DMA.
a 31-bit something rather different.