linux-kernel - Re: [LSF/MM TOPIC NOTES] x86 ZONE

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Message-ID: <20180428083303.GB31684@infradead.org>
Date:   Sat, 28 Apr 2018 01:33:03 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Christopher Lameter <cl@...ux.com>
Cc:     Michal Hocko <mhocko@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>, linux-mm@...ck.org,
        Jan Kara <jack@...e.cz>, matthew@....cx, x86@...nel.org,
        luto@...capital.net, martin.petersen@...cle.com,
        jthumshirn@...e.de, broonie@...nel.org, linux-spi@...r.kernel.org,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        "lsf-pc@...ts.linux-foundation.org" 
        <lsf-pc@...ts.linux-foundation.org>
Subject: Re: [LSF/MM TOPIC NOTES] x86 ZONE_DMA love

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.