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Date:   Sat, 28 Apr 2018 01:33:03 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Christopher Lameter <cl@linux.com>
Cc:     Michal Hocko <mhocko@kernel.org>,
        Christoph Hellwig <hch@infradead.org>,
        "Luis R. Rodriguez" <mcgrof@kernel.org>, linux-mm@kvack.org,
        Jan Kara <jack@suse.cz>, matthew@wil.cx, x86@kernel.org,
        luto@amacapital.net, martin.petersen@oracle.com,
        jthumshirn@suse.de, broonie@kernel.org, linux-spi@vger.kernel.org,
        linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org,
        "lsf-pc@lists.linux-foundation.org" 
        <lsf-pc@lists.linux-foundation.org>
Subject: Re: [LSF/MM TOPIC NOTES] x86 ZONE_DMA love
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On Fri, Apr 27, 2018 at 11:07:07AM -0500, Christopher Lameter wrote:
> Well it looks like what we are using it for is to force allocation from
> low physical memory if we fail to obtain proper memory through a normal
> channel.  The use of ZONE_DMA is only there for emergency purposes.
> I think we could subsitute ZONE_DMA32 on x87 without a problem.
> 
> Which means that ZONE_DMA has no purpose anymore.
> 
> Can we make ZONE_DMA on x86 refer to the low 32 bit physical addresses
> instead and remove ZONE_DMA32?

While < 32-bit allocations are much more common there are plenty
of requirements for < 24-bit or other weird masks still.