linux-kernel - Re: [PATCH 00/22] Don't use kmalloc() with GFP

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Date:   Thu, 24 Feb 2022 07:33:30 +0100
From:   Christoph Hellwig <hch@....de>
To:     Heiko Carstens <hca@...ux.ibm.com>
Cc:     Christoph Hellwig <hch@....de>, Baoquan He <bhe@...hat.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, cl@...ux.com, 42.hyeyoo@...il.com,
        penberg@...nel.org, rientjes@...gle.com, iamjoonsoo.kim@....com,
        vbabka@...e.cz, David.Laight@...lab.com, david@...hat.com,
        herbert@...dor.apana.org.au, davem@...emloft.net,
        linux-crypto@...r.kernel.org, steffen.klassert@...unet.com,
        netdev@...r.kernel.org, gor@...ux.ibm.com, agordeev@...ux.ibm.com,
        borntraeger@...ux.ibm.com, svens@...ux.ibm.com,
        linux-s390@...r.kernel.org, michael@...le.cc,
        linux-i2c@...r.kernel.org, wsa@...nel.org,
        Halil Pasic <pasic@...ux.ibm.com>,
        Vineeth Vijayan <vneethv@...ux.ibm.com>
Subject: Re: [PATCH 00/22] Don't use kmalloc() with GFP_DMA

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.